Segment Routing (SR) is a source routing technology. The source node selects a path for packet forwarding, and then encodes the path in the packet header as an ordered list of segments. Each segment is identified by the Segment Identifier (SID). The SR nodes along the path forward the packets based on the SIDs in the packets. Only the source node needs to maintain the path status.

IPv6 SR (SRv6) uses IPv6 addresses as SIDs to forward packets.

Basic concepts

SR node roles

An SR node is a node that supports the SRv6 feature. The following SR nodes are available:

· Source node—Responsible for inserting an SRH into the IPv6 header of IPv6 packets, or encapsulating an outer IPv6 header into IPv6 packets and inserting an SRH into the outer IPv6 header. A source node steers traffic to the SRv6 path defined in the Segment List of SRH.

¡ If the Segment List contains only one SID and the SRH is not required to include information or TLV, the source node only sets the SID as the destination address in the IPv6 header. No SRH is inserted.

¡ If the Segment List contains multiple SIDs, the source node must insert an SRH to the packets.

A source node can be the originator of SRv6 packets or the edge device of an SRv6 domain.

· Transit node—Forwards IPv6 packets along the SRv6 path. A transit node does not participate in SRv6 processing. It can be an SRv6-aware or SRv6-unaware node.

· Endpoint node—Performs an SRv6 function for received SRv6 packets. The IPv6 destination address of the received SRv6 packets must be an SRv6 SID configured on the endpoint node. The endpoint node processes the packets based on the SRv6 SID and updates the SRH.

A node can act as the source node in one SRv6 path and a transit node or endpoint node in another SRv6 path.

SID portions

SRv6 supports SRv6 SIDs that have specific functions.

An SRv6 SID is in the format of IPv6 address, but the IPv6 address does not belong to any interface on any device.

As shown in Figure 1, an SRv6 SID contains the Locator, Function, Arguments, and Must be zero (MBZ) portions.

· Locator—Identifies the network segment of the SID. An SRv6 node advertises IPv6 segments identified by locators to the network through routing protocols such as IGP to help other devices forward packets to that SRv6 node. Therefore, locators are typically used for SRv6 routing and addressing. The locator of an SRv6 SID must be unique in the SR domain.

· Function—Contains an opcode that identifies the network function of an SID. When an SRv6 node receives an SRv6 packet and detects that the IPv6 destination address matches an SRv6 SID in the local SID table, the node analyzes the Function field. Then, it locates and executes the corresponding operation for the function. Assume that an SRv6 node is configured with the opcode 101 end-x interface A command, which indicates that the Function portion of the SRv6 SID is set to 101, corresponding to the End.X operation instruction on the device. If the destination address of the SRv6 packet matches this local SRv6 SID, the node carries out the forwarding behavior associated with the End.X instruction, which is forwarding the packet from interface A identified by End.X.

· Arguments—Defines flow and service parameters for SRv6 packets, an optional field in SRv6 SIDs.

· MBZ—When the total number of bits in the Locator, Function, and Arguments portions is less than 128 bits, the lowest bits are padded with 0s.

Figure 1 SRv6 SID

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All SRv6 SIDs are allocated by the locator configured by the locator command. Therefore, SRv6 SIDs are divided into the following categories for a locator depending on the locator type and length:

· Common locators

Figure 2 Common locator

· Common locators can allocate common SRv6 SIDs, and common SRv6 SIDs include static and dynamic SRv6 SIDs. The formats are as follows:

¡ A static SRv6 SID is generated based on the following formula: static SRv6 SID = ipv6-prefix + 0 + opcode + 0.

- The ipv6-prefix portion represents the IPv6 prefix specified by using the ipv6-address and prefix-length arguments in the locator command. The number of bits occupied by the IPv6 prefix is configured by using the prefix-length argument.

- The number of bits occupied by 0s (following the ipv6-prefix portion) is 128 - prefix-length - static-length - args-length.

- opcode represents the static portion in the Function field. The number of bits occupied by the opcode is the value of the static-length argument. The number of bits occupied by 0s (following the opcode portion) is the value of the args-length argument.

¡ A dynamic SRv6 SID is generated based on the following formula: dynamic SRv6 SID = ipv6-prefix + dynamic + static + 0.

- dynamic represents the dynamic portion in the Function field. The value for this portion cannot be all zeros. The number of bits occupied by this portion is 128 - prefix-length - static-length - args-length.

- static represents the static portion in the Function field. The number of bits occupied by this portion is static-length. This portion can use any value. The number of bits occupied by 0s is the value of the args-length argument.

For example, use the locator test1 ipv6-prefix 100:200:DB8:ABCD:: 64 static 24 args 32 command.

¡ The locator is 100:200:DB8:ABCD::. The length is 64 bits.

¡ The static portion length is 24 bits.

¡ The Args portion length is 32 bits.

¡ The dynamic portion length is 8 bits.

In this example, the following non-compressible static SRv6 SID range and dynamic SRv6 SID range are obtained on the locator:

¡ The start value for static SRv6 SIDs is 100:200:DB8:ABCD:0:1::.

¡ The end value for static SRv6 SIDs is 100:200:DB8:ABCD:FF:FFFF::.

¡ The start value for dynamic SRv6 SIDs is 100:200:DB8:ABCD:100::.

¡ The end value for dynamic SRv6 SIDs is 100:200:DB8:ABCD:FFFF:FFFF::.

· COC32 locators

Figure 3 COC32 locator

COC32 locators are used for G-SRv6 compression. A COC locator can allocate SRv6 SIDs that carry COC flavors, End(COC32) SIDs and End.X(COC32) SIDs, and common SRv6 SIDs that do not carry COC flavors. For more information about COC flavors and G-SRv6, see "G-SRv6." You can specify these SRv6 SIDs in a static segment or use IGP to automatically allocate compressible SRv6 SIDs in a dynamic segment. Assume that you configure the locator test1 ipv6-prefix 100:200:DB8:ABCD:: 64 common-prefix 48 coc32 static 8 args 16 command. The G-SID contains the node ID, dynamic portion, and static portion, with a fixed length of 32 bits. In this case, the total length of the SRv6 SID is less than 128 bits, and the last 32 bits are MBZ, all set to 0. In this command:

¡ The locator is 100:200:DB8:ABCD::. The length is 64 bits.

¡ The common prefix length is 48 bits. A compressed SRv6 SID does not contain this portion.

¡ The static portion length is 8 bits.

¡ The Args portion length is 16 bits.

¡ The dynamic portion length is 8 bits.

¡ The MBZ is 32 bits.

In this example, the following compressible static SRv6 SID range and dynamic SRv6 SID range are obtained on the locator:

¡ The start value for static SRv6 SIDs is 100:200:DB8:ABCD:1::.

¡ The end value for static SRv6 SIDs is 100:200:DB8:ABCD:FF::.

¡ The start value for dynamic SRv6 SIDs is 100:200:DB8:ABCD:100::.

¡ The end value for dynamic SRv6 SIDs is 100:200:DB8:ABCD:FFFF::.

· COC-both locators

Figure 4 COC-both locator

For more flexible allocation of SRv6 SIDs, a new locator type COC-both has been introduced. In a COC-both locator, compressible SID portions and non-compressible SID portions are available. SIDs that carry COC flavors, for example, End(COC32) and End.X(COC32) SIDs are dynamically or statically allocated from the compressible SID portions. SIDs that do not carry COC flavors, for example, End(COCNONE) and End.X(COCNONE) SIDs are also dynamically or statically allocated from the compressible SID portions. Only common SIDs, such as End and End.X SIDs are allocated from the non-compressible SID portions. The SRv6 SIDs allocated from different portions are categorized as follows:

¡ SRv6 SIDs allocated from the static compressible portion.

¡ SRv6 SIDs allocated from the dynamic compressible portion.

¡ SRv6 SIDs allocated from the static non-compressible portion.

¡ SRv6 SIDs allocated from the dynamic non-compressible portion.

Assume that you configure the locator test1 ipv6-prefix 100:200:DB8:ABCD:: 64 common-prefix 48 coc-both non-compress-static 16 static 8 args 16 command.

¡ The locator is 100:200:DB8:ABCD::. The length is 64 bits.

¡ The common prefix length is 48 bits. A compressed SRv6 SID does not contain this portion.

¡ The compressible static portion length is 8 bits.

¡ The compressible dynamic portion length is 8 bits. This value is calculated by using the following formula: 32 – (prefix-length – common-prefix-length) + compressible-static-length.

¡ The non-compressible static portion length is 16 bits.

¡ The non-compressible dynamic portion length is 16 bits. This value is calculated by using the following formula: 128 – common-prefix-length – args-length – 32 – non-compressible-static-length.

¡ The Args portion length is 16 bits.

In this example, the following static compressible SRv6 SID range and dynamic compressible SRv6 SID range are obtained on the locator:

¡ The start value for compressible static SRv6 SIDs is 100:200:DB8:ABCD:1::.

¡ The end value for compressible static SRv6 SIDs is 100:200:DB8:ABCD:FF::.

¡ The start value for compressible dynamic SRv6 SIDs is 100:200:DB8:ABCD:100::.

¡ The end value for compressible dynamic SRv6 SIDs is 100:200:DB8:ABCD:FFFF::.

The following static non-compressible SRv6 SID range and dynamic non-compressible SRv6 SID range are obtained on the locator:

¡ The start value for static non-compressible SRv6 SIDs is 100:200:DB8:ABCD::1:0.

¡ The end value for static non-compressible SRv6 SIDs is 100:200:DB8:ABCD::FFFF:0.

¡ The start value for dynamic non-compressible SRv6 SIDs is 100:200:DB8:ABCD:0:1::.

¡ The end value for dynamic non-compressible SRv6 SIDs is 100:200:DB8:ABCD:0:FFFF:FFFF:0.

SRv6 endpoint behaviors

The local instruction identified by the Function field of an SRv6 SID is a node behavior that guides packet forwarding and processing. This local instruction is called SRv6 endpoint behavior. RFC 8986 defines opcode values for most types of node behaviors. From a network configuration perspective, different node forwarding behaviors are SRv6 SIDs with various functional types. The types of SRv6 SID include, but are not limited to the following:

· End SID—Identifies a node in the network, representing the prefix of a destination address. Upon arrival of packets at the node, if the SL is greater than 0, the node behavior is to decrease the SL by 1, extract the next SID from the SRH to update the destination address field in the IPv6 header, search for the routing table, and then forward the packet.

· End.X SID—Identifies a link in the network. Upon arrival of packets at the node that generated the SID, if the SL is greater than 0, the node behavior is to decrease the SL by 1, extract the next SID from the SRH to update the IPv6 header's destination address field, and then forward the packet from the link identified by the End.X SID.

· End.DT4 SID—Similar to a private network label in an MPLS L3VPN network, it identifies an IPv4 VPN instance in the network. The function of an End.DT4 SID is decapsulating packets and searching the routing table of the corresponding IPv4 VPN instance to forward the packets. End.DT4 SIDs are applicable to IPv4 private network access scenarios.

· End.DT6 SID—Similar to a private network label in an MPLS L3VPN network, it identifies an IPv6 VPN instance in the network. The function of an End.DT6 SID is decapsulating packets and searching the routing table of the corresponding IPv6 VPN instance to forward the packets. End.DT6 SIDs are applicable to IPv6 private network access scenarios.

· End.DT46 SID—Similar to a private network label in an MPLS L3VPN network, it identifies an IPv4 or IPv6 VPN instance in the network. End.DT46 SIDs are applicable to IPv4 and IPv6 private network concurrent access scenarios.

· End.DX4 SID—Identifies an IPv4 next hop from a PE to a CE in an IPv4 VPN instance in the network. The function of an End.DX4 SID is decapsulating packets and forwarding the decapsulated IPv4 packets out of the Layer 3 interface bound to the SID to a specific next hop. End.DX4 SIDs are applicable to IPv4 private network access scenarios.

· End.DX6 SID—Identifies an IPv6 next hop from a PE to a CE in an IPv6 VPN instance in the network. The function of an End.DX6 SID is decapsulating packets and forwarding the decapsulated IPv6 packets out of the Layer 3 interface bound to the SID to a specific next hop. End.DX6 SIDs are applicable to IPv6 private network access scenarios.

· End.DX2 SID—Identifies one end of a Layer 2 cross-connect in the EVPN VPWS over SRv6 scenario. The function of an End.DX2 SID is decapsulating packets and forwarding the decapsulated packets to the output interface of the SID.

· End.DX2L SID—Identifies packets that come from a bypass SRv6 PW. The packets will not be forwarded back to the bypass SRv6 PW for loop prevention. The function of an End.DX2L SID is removing the outer IPv6 header and SRH of packets and forwarding the decapsulated packets to the output interface of the SID. End.DX2L SIDs are applicable to EVPN VPWS over SRv6 multihomed sites.

· End.DT2M SID—Identifies one end of a Layer 2 cross-connect for EVPN VPLS over SRv6 BUM traffic and floods traffic. The function of an End.DT2M SID is decapsulating packets and flooding the decapsulated packets in the VSI.

· End.DT2U SID—Identifies one end of a Layer 2 cross-connect and performs unicast forwarding. The function of an End.DT2U SID is removing the outer IPv6 header and SRH of packets, looking up the MAC address table for the destination MAC address, and forwarding the packets to the output interface based on the MAC address entry. End.DT2U SIDs are applicable to EVPN VPLS unicast traffic.

· End.DT2UL SID—Identifies packets that come from a bypass SRv6 PW. The packets will not be forwarded back to the bypass SRv6 PW for loop prevention. The function of an End.DT2UL SID is removing the outer IPv6 header and SRH of packets and forwarding the packets to the output interface through destination MAC address lookup. End.DT2UL SIDs are applicable to EVPN VPLS over SRv6 multihomed sites.

· End.OP SID—Applies to the SRv6 OAM scenario. For more information about End.OP SIDs, see "Configuring SRv6 OAM."

· End.B6.Encaps—Applies to the scenario where an SRv6 ingress node steers traffic to an SRv6 TE policy or stitches an SRv6 TE policy by using a BSID. The node behavior is to encapsulate a new IPv6 header and SRH onto the received packet.

· End.B6.Encaps.Red—Applies to the scenario where an SRv6 ingress node steers traffic to an SRv6 TE policy or stitches an SRv6 TE policy by using a BSID. The node behavior is to encapsulate the SIDs except for the first SID in the SRv6 TE policy’s SID list when it encapsulates an IPv6 header and SRH onto the received packet to reduce the SRH length.

· End.B6.Insert—Applies to the scenario where an SRv6 ingress node steers traffic to an SRv6 TE policy or stitches an SRv6 TE policy by using a BSID. The node behavior is to encapsulate an SRH header onto the received packet.

· End.B6.Insert.Red—Applies to the scenario where an SRv6 ingress node steers traffic to an SRv6 TE policy or stitches an SRv6 TE policy by using a BSID. The node behavior is to insert an SRH into the received IPv6 packet and to encapsulate the SIDs except for the first SID in the SRv6 TE policy’s SID list to reduce the SRH length.

· Src.DT4 SID—Identifies the source address for a BIERv6 tunnel in an IPv4 multicast VPN. In BIER multicast VPN scenarios, the forwarding action is to decapsulate the packet and look up IPv4 table entries. For more information about BIERv6 tunnel source addresses, see "Configuring multicast VPN" in IP Multicast Configuration Guide.

· Src.DT6 SID—Identifies the source address for a BIERv6 tunnel in an IPv6 multicast VPN. In BIER multicast VPN scenarios, the forwarding action is to decapsulate the packet and look up IPv6 table entries. For more information about BIERv6 tunnel source addresses, see "Configuring multicast VPN" in IP Multicast Configuration Guide.

· End.BIER SID—Applies to BIERv6 scenarios. For more information about End.BIER SIDs, see "Configuring BIER" in BIER Configuration Guide.

· End.RGB SID—Used in MSR6 scenarios. For more information about End.RGB SIDs, see "Configuring BIER" in BIER Configuration Guide.

Use IGP to advertise SRv6 SIDs for an SR node. The other SR nodes will generate route entries of that SR node based on the advertised information.

SRv6 SID flavors

SID flavors can be combined with some node behaviors to form new node behaviors. For example, node behavior End.X can be combined flavor PSP to form a new node behavior called End.X with PSP. Use SRv6 SID flavors to change the forwarding behaviors of SRv6 SIDs to meet multiple service requirements. The following SRv6 SID flavors are supported:

· NO-FLAVOR—The SRv6 SID does not carry any flavors.

· Penultimate Segment POP of the SRH (PSP)—The penultimate SRv6 node removes the SRH to reduce the workload of the end SRv6 node and improve the forwarding efficiency. The end SRv6 node does not read the SRH, and it only looks up the local SID table for the destination IPv6 address of packets to forward the packets.

· NO PSP—The penultimate SRv6 node does not remove the SRH. For correct connectivity detection in the SRv6 OAM scenario, make sure the SRH is not removed on the penultimate SRv6 node. The device needs to obtain the SID from the SRH to identify the link connectivity.

· Ultimate Segment POP of the SRH (USP)—The ultimate SRv6 node (endpoint node) removes the SRH from the packets. In an SRv6 VPN network, upon obtaining the forwarding action based on the SID, the PE removes the SRH from the packets and forwards the packets to the CE.

· Ultimate Segment Decapsulation (USD)—The ultimate SRv6 node (endpoint node) removes the outer IPv6 header from the packets. In the TI-LFA scenario, the endpoint node in the repair list removes the outer IPv6 header from the packets and forwards the decapsulated packets to the destination node.

· Continue of Compression (COC)—The SID next to the current SID is a G-SID. A G-SID is used in a compression scenario to reduce the length of SRH.

The device supports advertising SRv6 SIDs with the following flavor types through IGP or BGP:

· NO-FLAVOR

· PSP

· PSP&USP&USD

· COC

Local SID forwarding table

An SRv6-enabled node maintains a local SID forwarding table that records the SRv6 SIDs generated on the local node. The local SID forwarding table has the following functions:

· Stores local generated SRv6 SID forwarding information.

· Stores SRv6 SID operation types.

Segment List

A Segment List is an ordered list of SIDs, which is also referred to as a Segment Identifier (SID) list in this document. The SR nodes forward packets based on the SIDs in the order that they are arranged in the SID list.

SRv6 tunnel

An SRv6 tunnel is a virtual point-to-point connection established between the SRv6 ingress node and egress node. IPv6 packets are encapsulated at the ingress node and de-encapsulated at the egress node.

SRv6 packet format

An outer IPv6 header and a Segment Routing Header (SRH) are added to the original Layer 3 data packet to form an SRv6 packet.

As shown in Figure 5, the value for the Next Header field is 43 in the outer IPv6 header, which indicates that the header next to the IPv6 header is a routing extension header. The value for the Routing Type field in the routing extension header is 4, which indicates that the routing extension header is an SRH. The SRH header contains the following fields:

· 8-bit Next Header—Identifies the type of the header next to the SRH.

· 8-bit Hdr Ext Len—Length of the SRH header in 8-octet units, not including the first 8 octets.

· 8-bit Routing Type—The value for this field is 4, which represents SRH.

· 8-bit Segments Left—Contains the index of the next segment to inspect in the Segment List. The Segments Left field is set to n-1 where n is the number of segments in the Segment List. Segments Left is decremented at each segment.

· 8-bit Last Entry—Contains the index of the first SID in the path used to forward the packet.

· 8-bit Flags—Contains flags.

· 16-bit Tag—Tags a packet as part of a class or group of packets, for example, packets sharing the same set of properties.

· Segment List—Contains 128-bit IPv6 addresses representing the ordered segments. The Segment List is encoded starting from the last segment of the path. The first element of the segment list (Segment List [0]) contains the last segment of the path, the second element (Segment List [1]) contains the penultimate segment of the path and so on. The number enclosed in a pair of brackets is the index of a segment.

Figure 5 SRv6 packet format

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SRv6 packet forwarding

As shown in Figure 6, a source node receives a packet that matches an SRv6 path. Device A is the source node, Device C and Device E are endpoint nodes, and Device B and Device D are transit nodes. The packet is forwarded through the SRv6 path as follows:

1. Upon receiving an IPv6 packet, Device A performs the following operations:

a. Encapsulates an SRH to the packet. The packet must pass two segments to reach Device E, so the Segments Left (SL) in the SRH is set to 1 (the number of segments along the path minus 1). The Segment List contains Segment List [0]=E and Segment List [1]=C.

b. Encapsulates an outer IPv6 header to the packet. The source address of the IPv6 header is an IP address on Device A and the destination address is determined by the SL value. On Device A, the SL value is 1, which points to the SID on Device C, so the destination address is the SID on Device C.

c. Looks up the routing table based on the destination address of the outer IPv6 header and forwards the packet to Device B.

2. Device B looks up the routing table based on the destination address of the outer IPv6 header and forwards the packet to Device C.

3. Device C performs the following operations:

a. Checks the SL value in the SRH and decreases the value by 1 if the SL value is greater than 0.

b. Updates the destination address to the address pointed by the SL. In this example, the SL is 0, which points to the SID on Device E. Device C replaces the destination address in the outer IPv6 header with the SID on Device E.

c. Looks up the routing table based on the destination address of the outer IPv6 header and forwards the packet to Device D.

4. Device D looks up the routing table based on the destination address of the outer IPv6 header and forwards the packet to Device E.

5. Device E checks the SL value in the SRH and finds that the value has decreased to 0. The device performs the following operations:

a. Decapsulates the packet by removing the outer IPv6 header and the SRH.

b. Forwards the original packet to the destination based on the destination address.

Figure 6 SRv6 packet forwarding

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Directing traffic to an SRv6 tunnel

After an SRv6 tunnel is established, traffic is not forwarded on the tunnel automatically. You must direct the traffic to the tunnel by configuring a static route or automatic route advertisement.

Static routing

You can direct traffic to an SRv6 tunnel by creating a static route that reaches the destination through the tunnel interface on the source node. This is the easiest way to implement SRv6 tunnel forwarding. When traffic to multiple networks is to be forwarded through the SRv6 tunnel, you must configure multiple static routes, resulting in increased configuration and maintenance workloads.

For more information about static routing, see Layer 3—IP Routing Configuration Guide.

Automatic route advertisement

Automatic route advertisement distributes the SRv6 tunnel to the IGP (OSPF or IS-IS), so the SRv6 tunnel can participate in IGP route calculation. Automatic route advertisement is easy to configure and maintain.

Automatic route advertisement can be implemented by using the following methods:

· IGP shortcut—Also known as AutoRoute Announce. It considers the SRv6 tunnel as a link that directly connects the tunnel ingress node and the egress node. Only the ingress node uses the SRv6 tunnel during IGP route calculation.

· Forwarding adjacency—Considers the SRv6 tunnel as a link that directly connects the tunnel ingress node and the egress node, and advertises the link to the network through an IGP. Every node in the network uses the SRv6 tunnel during IGP route calculation.

IMPORTANT:

Only IGP shortcut is supported in the current software version.

As shown in Figure 7, an SRv6 tunnel exists from Device D to Device C. IGP shortcut enables only the ingress node Device D to use the SRv6 tunnel in IGP route calculation. Device A cannot use this tunnel to reach Device C. With forwarding adjacency enabled, Device A can learn this SRv6 tunnel and transfer traffic to Device C by forwarding the traffic to Device D.

Figure 7 IGP shortcut and forwarding adjacency diagram

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G-SRv6

Background

In an SRv6 TE policy scenario, the administrator needs to add the 128-bit SRv6 SIDs of SRv6 nodes on the packet forwarding path into the SID list of the SRv6 TE policy. If the packet forwarding path is long, a large number of SRv6 SIDs will be added to the SID list of the SRv6 TE policy. This greatly increases the size of the SRv6 packet header, resulting in low device forwarding efficiency and reduced chip processing speed. The situation might be worse in a scenario that spans across multiple ASs where a much greater number of end-to-end SRv6 SIDs exist.

Generalized SRv6 (G-SRv6) encapsulates shorter SRv6 SIDs (G-SIDs) in the segment list of SRH by compressing the 128-bit SRv6 SIDs. This reduces the size of the SRv6 packet header and improves the efficiency for forwarding SRv6 packets. In addition, G-SRv6 supports both 128-bit SRv6 SIDs and G-SIDs in a segment list.

About G-SRv6

Typically, an address space is reserved for SRv6 SID allocation in an SRv6 subnet. This address space is called an SID space. In the SRv6 subnet, all SIDs are allocated from the SID space. The SIDs have the same prefix (common prefix). The SID common prefix is redundant information in the SRH.

G-SRv6 removes the common prefix and carries only the variable portion of SRv6 SIDs (G-SIDs) in the segment list, effectively reducing the SRv6 packet header size. To forward a packet according to routing table lookup, SRv6 replaces the destination IP address of the packet with the combination of the G-SID and common prefix in the segment list of the SRH.

With the compression efficiency and network scale taken into consideration, the ideal length of SRv6 SIDs is 32 bits after compression through G-SRv6.

G-SID format

As shown in Figure 8, the locator portion of an SRv6 SID contains the Common Prefix and Node ID portions. The Common Prefix portion represents the address of the common prefix. The Node ID portion identifies a node. G-SRv6 can compress all SIDs with the same common prefix into 32-bit G-SIDs. A G-SID contains the Node ID and Function portions of a 128-bit SRv6 SID. A 128-bit SRv6 SID is formed by the Common Prefix portion, a 32-bit G-SID, and the 0 (Args&MBZ) portion.

Figure 8 Compressible SRv6 SID

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G-SRv6 packet

G-SRv6 packet format

As shown in Figure 9, G-SRv6 can encapsulate both G-SIDs and 128-bit SRv6 SIDs in the segment list of the SRH. It needs to encapsulate four G-SIDs in a group to the original location of a 128-bit SRv6 SID. If the location contains fewer than four G-SIDs (less than 128 bits), G-SRv6 pads the remaining bits with 0s. Multiple consecutive G-SIDs form a compressed path, called a G-SID list. A G-SID list can contain one or more groups of G-SIDs.

Figure 9 G-SRv6 packet format

NOTE:

If the SRv6 SID of the next node requires compression, the routing protocol adds the Continue of Compression (COC) flag to the advertised SRv6 SID of the local node. The COC flag indicates that the next SRv6 SID is a G-SID. A COC flag only identifies the forwarding behavior of an SRv6 SID, and is not actually carried in the packet. The COC flags in Figure 9 are for illustration purposes only.

The G-SIDs in the segment list are arranged as follows:

· The SRv6 SID before the G-SID list is a 128-bit SRv6 SID with the COC flag, indicating that the next SID is a 32-bit G-SID.

· Except the last G-SID, all G-SIDs in the G-SID list must carry the COC flag to indicate that the next SID is a 32-bit G-SID.

· The last G-SID in the G-SID list must be a 32-bit G-SID without the COC flag, indicating that the next SID is a 128-bit SRv6 SID.

· The next SRv6 SID after the G-SID list is a 128-bit SRv6 SID that can carry the COC flag or does not carry the COC flag.

Calculating the destination address with G-SID

As shown in Figure 10, G-SRv6 combines the G-SID and Common Prefix in the segment list to form a new destination address.

· Common Prefix—Common prefix address manually configured by the administrator.

· G-SID—Compressed 32-bit SID obtained from the SRH.

· SID Index (SI)—Index that identifies a G-SID in a group of G-SIDs. This field is the least significant two bits of the destination IPv6 address. The value range is 0 to 3. The SI value decreases by 1 at each node that performs SID compression. If the SI value becomes 0, the SL value decreases by 1. In a group of G-SIDs in the segment list, the G-SIDs are arranged from left to right based on SI values. The SI value is 0 for the leftmost G-SID, and is 3 for the rightmost G-SID.

· 0—If the total length of the Common Prefix, G-SID, and SI portions is less than 128 bits, the deficient bits are padded with 0s before the SI portion.

Figure 10 Destination address calculated with G-SID

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Suppose the following conditions exist:

· The Common Prefix deployed on the SRv6 node is A:0:0:0::/64.

· The G-SID in the SRv6 packet is 1:1.

· The SI value associated with the G-SID is 3.

Based on the previous conditions, the device calculates the destination address as A:0:0:0:1:1::3.

Upon receiving the G-SRv6 packet, the SRv6 node calculates the destination address for the packet as follows:

· If the destination address of the packet is a 128-bit SRv6 SID with the COC flag in the segment list, the next SID is a G-SID. The device decreases the SI value by 1 and searches for the G-SID group corresponding to [SI-1]. Then, the device calculates the destination address based on the 32-bit G-SID identified by SI value 3.

· If the destination address of the packet is a 32-bit SRv6 SID with the COC flag in the segment list, the next SID is a G-SID.

¡ If the SI value is larger than 0, the device decreases the SI value by 1 and searches for the G-SID group corresponding to SL value of the packet. Then, the device calculates the destination address based on the 32-bit G-SID identified by [SI-1].

¡ If the SI value is equal to 0, the device decreases the SL value by 1, resets the SI value to 3, and searches for the G-SID group corresponding to the SL value of the packet. Then, the device calculates the destination address based on the 32-bit G-SID identified by SI value 3.

· If the destination address of the packet is a 32-bit SRv6 SID without the COC flag in the segment list, the device decreases the SL value by 1 and searches for the 128-bit SRv6 SID corresponding to [SL-1]. Then, the device replaces the destination address in the IPv6 header with the SRv6 SID.

· If the destination address of the packet is a 128-bit SRv6 SID without the COC flag in the segment list, the device decreases the SL value by 1 and searches for the 128-bit SRv6 SID corresponding to [SL-1]. Then, the device replaces the destination address in the IPv6 header with the SRv6 SID.

Topology-Independent Loop-Free Alternate Fast Re-Route (TI-LFA FRR)

Topology-Independent Loop-Free Alternate Fast Re-Route (TI-LFA FRR) provides link and node protection for SRv6 tunnels. When a link or node fails, TI-LFA FRR switches the traffic to the backup path to ensure continuous data forwarding.

TI-LFA FRR background

To minimize traffic loss during the route reconvergence process in SR-MPLS, you can enable the FRR feature on the device directly connected to the protected link or node. The device enabled with FRR is called the Point of Local Repair (PLR). The PLR calculates the shortest path to the destination and calculates an FRR backup path at the same time, and then writes the information into the FIB table. When a protected link or node fails, traffic is rerouted through the FRR backup path on the PLR node, without the need for the network topology to reconverge, significantly reducing traffic loss. FRR has the following mechanisms:

· Loop-Free Alternate Fast Reroute (LFA FRR)—To calculate the backup path, LFA FRR identifies a protected neighboring node (LFA node) of the PLR, enabling traffic to be forwarded to the destination node without passing through the protected link or node. In some scenarios, especially in a ring network, LFA FRR cannot calculate a backup path, making it topology dependent. According to RFC 6571, LFA FRR has a topology coverage of 80% to 90%.

· Remote Loop-Free Alternate Fast Reroute (RLFA FRR)—To improve the topology coverage of LFA FRR, RFC 7490 defines RLFA FRR, which enables traffic to be forwarded from the PLR to an RLFA FRR node and reach the destination node without passing through the protected link or node. Compared to LFA FRR, RLFA FRR does not restrict the protective node to being a neighbor of the PLR, providing more protection possibilities and increasing the topology coverage to 95% to 99%.

· TI-LFA FRR suitable for SRv6 and SR-MPLS—Compared to LFA FRR and RLFA FRR, TI-LFA FRR is topology independent, meaning FRR backup path calculation is not restricted by the network topology. PLR can automatically calculate a TI-LFA FRR backup path as long as a bypass forwarding path is available.

As shown in Figure 11, node A sends data packets to node F. When the link between node B and node E fails, node B forwards the data packets to node C. The cost of the link between node C and node D is 100 (which is greater than the cost of the link between node C and node D) and the routes on node C have not converged. As a result, node C determines that the next hop of the optimal path to reach node F is node B. Then, node C forwards the data packets back to node B, which causes a loop.

Figure 11 TI-LFA application scenario

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To resolve this issue, deploy TI-FLA on the SRv6 network. As shown in Figure 12, when the link between node B and node E fails, node B uses the backup path calculated by TI-LFA to forward the data packets along the B->C->D->E path.

Figure 12 TI-LFA forwarding network diagram

TI-LFA FRR concepts

TI-LFA FRR uses the concepts of RLFA FRR defined in RFC 7490:

· P space—A set of nodes reachable (using pre-convergence paths) from the PLR without using the protected link or node (including equal-cost path splits). Nodes in the P space are called P nodes.Calculation of P nodes typically involves building an SPF tree with the PLR as the root node, and then identifying nodes on the SPF tree that meet the loop-free requirement.

· Extended P space—A set of nodes reachable (using pre-convergence paths) from the neighbors of the PLR (except for the protected node) without using the protected link or node (including equal-cost path splits). The P space is a subset of the extended P space. Nodes in the extended P space are also called P nodes. Neighbor nodes of the PLR are N nodes. As shown in Figure 13, the expanded P space contains nodes Src, B, C, and D. The P nodes meet the following loop-free requirement: Distance (N, P) < Distance (N, PLR) + Distance (PLR, P).

· Q space—A set of nodes that can reach (using pre-convergence paths) the destination without using the protected link or node (including equal-cost path splits). Nodes in the Q space are called Q nodes.

Figure 13 TI-LFA FRR concepts

TI-LFA FRR path calculation

As shown in Figure 14, PE 1 is the source node. P 1 is the faulty node. PE 2 is the destination node. The numbers on links represent the link costs. A data flow traverses PE 1, P 1, and PE 2. To protect data against P 1 failure, TI-LFA FRR calculates the extended P space, Q space, shortest path tree converged after P 1 fails, repair list, and backup output interface, and creates the backup forwarding entry.

TI-LFA FRR calculates the backup path by using the following steps:

1. Calculates the extended P space: P 2.

2. Calculates the Q space: PE 2 and P 4.

3. Calculates the shortest path tree converged after P 1 fails: PE 1 --> P 2 --> P 4 --> PE 2.

4. Calculates the repair list: End.X SID C of the link between P 2 and P 3 and End.X SID D of the link between P 3 and P 4.

5. Calculates the backup output interface, that is, the output interface to the next hop after the link from PE 1 to P 1 fails.

Figure 14 TI-LFA FRR diagram

TI-LFA FRR forwarding process

After TI-LFA FRR finishes backup path calculation, traffic will be switched to the backup path in response to a primary path failure.

As shown in Figure 15, P 2 is a P node and P 4 and PE 2 are Q nodes. When the next hop on the primary path (P 1) fails, TI-LFA FRR switches the traffic to the backup path. The following are the detailed steps:

1. PE 1 looks up the IPv6 routing table for the destination IPv6 address of a packet and finds that the next hop is P 2. PE 1 encapsulates the packet according to the repair list.

¡ Adds an SRH header. The SID list is Segment List [0]=D and Segment List [1]=C. The SIDs are arranged from the farthest node to the nearest node.

¡ Adds an outer IPv6 header. The source address is address A on source node PE 1 and the destination address is the address pointed by SL. Because the SL is 1, the destination address is C as pointed by Segment List [1].

2. After P2 receives the packet, it performs the following operations:

a. Checks the SL value in the SRH header and decreases the value by 1.

b. Searches for the address pointed by Segment List [0] and finds that the address is End.X SID D between P 3 and P 4.

c. Replaces the destination address in the outer IPv6 header with End.X SID D.

d. Obtains the output interface and next hop according to End.X SID C and forwards the encapsulated packet to P 3.

3. After P3 receives the packet, it performs the following operations:

a. Checks the SL value in the SRH header and finds that the SL value is 0.

b. Decapsulates the packet.

c. Obtains the output interface and next hop according to End.X SID D and forwards the packet to P 4.

4. After P4 receives the packet, it searches the IP routing table for the destination IP address of the packet and forwards the packet to PE 2.

Figure 15 Data forwarding over the TI-LFA FRR backup path

Microloop avoidance after a network failure

As shown in Figure 16, when Device B fails, traffic to Device C will be switched to the backup path calculated by TI-LFA. After Device A finishes route convergence, traffic will be switched to the post-convergence path. If Device D and Device F have not finished route convergence and still forward traffic along the pre-convergence path, a loop is formed between Device A and Device F. The loop exists until Device D and Device F finish route convergence.

FRR microloop avoidance and SR microloop avoidance can resolve this issue. After you configure TI-LFA, Device A first switches traffic to the backup path calculated by TI-LFA when Device B fails. Then, Device A waits for Device D and Device F to finish route convergence before starting route convergence. After Device A also finishes route convergence, Device A switches the traffic to the converged route.

Figure 16 Diagram for microloop avoidance after a network failure

SR microloop avoidance after a failure recovery

As shown in Figure 17, before the link between Device B and Device C recovers, traffic traverses along the backup path. After the link recovers, Device A forwards the traffic to Device B if Device A finishes route convergence before Device B. With route convergence unfinished, Device B still forwards the traffic along the backup path. A loop is formed between Device A and Device B.

SR microloop avoidance can resolve this issue. After the link recovers, SR microloop avoidance automatically calculates the optimal path from Device A to Device C and forwards traffic along the path. To forward a packet along the newly calculated path, Device A adds, for example, the adjacency SID from Device B to Device C, to the packet and then sends the packet to Device B. Then, Device B forwards the packet to Device C based on the path information.

Upon expiration of the microloop avoidance RIB-update-delay timer and completion of route convergence on Device B, Device A does not add path information to packets anymore. It will forward packets to Device C as usual.

Figure 17 Diagram for SR microloop avoidance after a failure recovery

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Protocols and standards

· draft-previdi-6man-segment-routing-header

· draft-ietf-6man-segment-routing-header

· draft-filsfils-spring-segment-routing

· draft-filsfils-spring-srv6-network-programming

SRv6 tasks at a glance

To configure SRv6, perform the following tasks:

1. Configuring SRv6 SIDs

¡ Configuring non-compressible SRv6 SIDs

¡ Configuring G-SIDs

This task is required if SRv6 compression is enabled.

¡ Configuring compressible and non-compressible hybrid SRv6 SIDs

2. (Optional.) Manage SRv6 SIDs

¡ Configuring dynamic End.X SID deletion delay

¡ Configuring the delay time to flush static End.X SIDs to the FIB

3. Using IGP to advertise SRv6 SIDs

4. Enabling BGP to advertise routes for a locator

This task is required in an inter-AS network.

5. (Optional.) Configuring TI-LFA FRR

6. (Optional.) Configuring the SRv6 MTU

7. (Optional.) Enabling SNMP notifications for SRv6

Prerequisites for SRv6

Before you configure an SRv6 tunnel, perform the following tasks:

· Determine the ingress node, transit nodes, and egress node of the SRv6 tunnel.

· Plan the IPv6 address of each SR node.

Configuring non-compressible SRv6 SIDs

Configuring the local locator and opcode

Restrictions and guidelines

Each locator must have a unique name.

Do not configure the same IPv6 address prefix and prefix length for different locators. In addition, the IPv6 address prefixes of different locators cannot overlap.

You cannot disable SRv6 or delete a locator in SRv6 view if the locator has dynamic SRv6 SIDs that are being used.

You can change a COC-both locator to a common locator or vice versa without deleting the configured locator but directly editing the command parameters, as follows:

· Change a common locator to a COC-both locator by adding the common-prefix and non-compress-static parameters. Other parameters cannot be edited.

For example, assume you configure a common locator as locator test ipv6-prefix 100:1:: 80 static 8 args 8. You can change the locator to a COC-both locator by executing locator test ipv6-prefix 100:1:: 80 common-prefix 64 coc-both non-compress-static 8 static 8 args 8.

· Change a COC-both locator to a common locator by deleting the common-prefix and non-compress-static parameters. Other parameters cannot be edited.

For example, assume you configure a COC-both locator as locator test ipv6-prefix 100:1:: 80 common-prefix 64 coc-both non-compress-static 8 static 8 args 8. You can change the locator to a common locator by executing locator test ipv6-prefix 100:1:: 80 static 8 args 8.

Procedure

1. Enter system view.

system-view

2. Enable SRv6 and enter SRv6 view.

segment-routing ipv6

3. Configure a locator and enter SRv6 locator view.

locator locator-name [ ipv6-prefix ipv6-address prefix-length [ args args-length | static static-length ] * ]

4. (Optional.) Enable anycast for the locator.

anycast enable

By default, anycast is disabled for a locator.

A locator is an anycast locator if the A-bit is set in the Flags field of the Locator TLV in routing protocol packets. An anycast locator is shared by a group of SRv6 nodes.

5. Configure an opcode. Perform one of the following tasks:

¡ Configure an opcode for End SIDs.

opcode { opcode | hex hex-opcode } end

¡ Configure an opcode for End.X SIDs.

opcode { opcode | hex hex-opcode } end-x interface interface-type interface-number nexthop nexthop-ipv6-address

For End.X SRv6 SIDs, if you specify a tunnel interface as the output interface, you can specify only tunnel interfaces in GRE over IPv4, IPsec over IPv4, or IPsec over IPv6 mode.

¡ Configure an opcode for End.DT4 SIDs.

opcode { opcode | hex hex-opcode } end-dt4 [ vpn-instance vpn-instance-name [ evpn | l3vpn-evpn ] ]

The specified VPN instance must exist. The same End.DT4 SID cannot be configured in different VPN instances.

¡ Configure an opcode for End.DT6 SIDs.

opcode { opcode | hex hex-opcode } end-dt6 [ vpn-instance vpn-instance-name [ evpn | l3vpn-evpn ] ]

The specified VPN instance must exist. The same End.DT6 SID cannot be configured in different VPN instances.

¡ Configure an opcode for End.DT46 SIDs.

opcode { opcode | hex hex-opcode } end-dt46 [ vpn-instance vpn-instance-name [ evpn | l3vpn-evpn ] ]

The specified VPN instance must exist. The same End.DT46 SID cannot be configured in different VPN instances.

¡ Configure an opcode for End.DX4 SIDs.

opcode { opcode | hex hex-opcode } end-dx4 interface interface-type interface-number nexthop nexthop-ipv4-address [ vpn-instance vpn-instance-name [ evpn ] ]

The specified VPN instance must exist. The same End.DX4 SID cannot be configured with different output interfaces or next hops.

¡ Configure an opcode for End.DX6 SIDs.

opcode { opcode | hex hex-opcode } end-dx6 interface interface-type interface-number nexthop nexthop-ipv6-address [ vpn-instance vpn-instance-name [ evpn ] ]

The specified VPN instance must exist. The same End.DX6 SID cannot be configured with different output interfaces or next hops.

¡ Configure an opcode for End.DX2 SIDs.

opcode { opcode | hex hex-opcode } end-dx2 xconnect-group group-name connection connection-name

The specified cross-connect group and cross-connect must exist.

opcode { opcode | hex hex-opcode } end-dx2 vsi vsi-name interface interface-type interface-number

The specified VSI must exist.

¡ Configure an opcode for End.DX2L SIDs.

opcode { opcode | hex hex-opcode } end-dx2l xconnect-group group-name connection connection-name

The specified cross-connect group and cross-connect must exist.

opcode { opcode | hex hex-opcode } end-dx2l vsi vsi-name interface interface-type interface-number

The specified VSI must exist.

¡ Configure an opcode for End.DT2M SIDs.

opcode { opcode | hex hex-opcode } end-dt2m vsi vsi-name

The specified VSI must exist. The same End.DT2M SID cannot be configured in different VSIs.

¡ Configure an opcode for End.DT2U SIDs.

opcode { opcode | hex hex-opcode } end-dt2u vsi vsi-name

The specified VSI must exist. The same End.DT2U SID cannot be configured in different VSIs.

¡ Configure an opcode for End.DT2UL SIDs.

opcode { opcode | hex hex-opcode } end-dt2ul vsi vsi-name

The specified VSI must exist. The same End.DT2UL SID cannot be configured in different VSIs.

¡ Configure an opcode for End.OP SIDs.

opcode { opcode | hex hex-opcode } end-op

Configuring G-SIDs

Restrictions and guidelines

The IPv6 prefix length must be longer than the common prefix length.

Procedure

1. Enter system view.

system-view

2. Enable SRv6 and enter SRv6 view.

segment-routing ipv6

3. Enable SRv6 compression.

srv6 compress enable

By default, SRv6 compression is disabled.

4. Configure a locator and enter SRv6 locator view.

locator locator-name [ ipv6-prefix ipv6-address prefix-length common-prefix common-prefix-length coc32 [ args args-length | static static-length ] * ]

5. Configure an opcode. Perform one of the following tasks:

¡ Configure an opcode for End SIDs.

opcode opcode end-coc32

¡ Configure an opcode for End.X SIDs.

opcode opcode end-x-coc32 interface interface-type interface-number nexthop nexthop-address

For End.X(COC32) SRv6 SIDs, if you specify a tunnel interface as the output interface, you can specify only tunnel interfaces in GRE over IPv4, IPsec over IPv4, or IPsec over IPv6 mode.

¡ Configure an opcode for other segments.

For more information, see "Configuring non-compressible SRv6 SIDs."

Configuring compressible and non-compressible hybrid SRv6 SIDs

Restrictions and guidelines

For a locator that has both compressible and non-compressible SRv6 SIDs, you can set the same opcode for the compressible and non-compressible hybrid SRv6 SIDs.

You can change a COC-both locator to a common locator or vice versa without deleting the configured locator but directly editing the command parameters, as follows:

· Change a common locator to a COC-both locator by adding the common-prefix and non-compress-static parameters. Other parameters cannot be edited.

· Change a COC-both locator to a common locator by deleting the common-prefix and non-compress-static parameters. Other parameters cannot be edited.

Procedure

1. Enter system view.

system-view

2. Enable SRv6 and enter SRv6 view.

segment-routing ipv6

3. Enable SRv6 compression.

srv6 compress enable

By default, SRv6 compression is disabled.

4. Configure a locator and enter SRv6 locator view.

locator locator-name [ ipv6-prefix ipv6-address prefix-length common-prefix common-prefix-length coc-both [ non-compress-static non-compress-static-length ] [ args args-length | static static-length ] * ]

5. (Optional.) Reserve SRv6 SIDs.

reserved-sid-start sid-value count reserved-sid-count

By default, no SRv6 SIDs are reserved.

When the device generates an SRv6 TE policy based on received SRv6 TE policy routes, it must assign a BSID to the SRv6 TE policy. Use this command to reserve SRv6 SIDs that can be assigned to SRv6 TE policies as BSIDs. The reserved SRv6 SIDs cannot be used by other protocols.

6. Configure an opcode. Perform one of the following tasks:

¡ Configure an opcode for End (COCNONE) SIDs.

opcode { opcode | hex hex-opcode } end-coc-none

End (COCNONE) SIDs are allocated from compressible SRv6 SID space. The SIDs have the same function as End SIDs.

¡ Configure an opcode for End.X (COCNONE) SIDs.

opcode { opcode | hex hex-opcode } end-x-coc-none interface interface-type interface-number nexthop nexthop-ipv6-address

End.X (COCNONE) SIDs are allocated from compressible SRv6 SID space. The SIDs have the same function as End.X SIDs.

For End.X(COCNONE) SRv6 SIDs, if you specify a tunnel interface as the output interface, you can specify only tunnel interfaces in GRE over IPv4, IPsec over IPv4, or IPsec over IPv6 mode.

¡ Configure an opcode for other segments.

For more information, see "Configuring non-compressible SRv6 SIDs."

Configuring dynamic End.X SID deletion delay

About this task

Packet loss occurs between OSPFv3 or IS-IS neighbors if the neighbors frequently delete and request dynamically allocated End.X SIDs for the links between them because of neighbor flapping. To resolve this issue, set a delay timer for deleting dynamically allocated End.X SIDs when the neighbors are disconnected. If the neighbors are still disconnected when the delay timer expires, the device deletes the dynamically allocated End.X SIDs.

Restrictions and guidelines

The device always immediately deletes automatically allocated End.X SIDs without any delay in the following situations:

· The reset ospfv3 process command is executed. For more information about this command, see OSPFv3 commands in Layer 3—IP Routing Command Reference.

· The reset isis all command is executed. For more information about this command, see IS-IS commands in Layer 3—IP Routing Command Reference.

· Interfaces are deleted or removed. For example, an interface module is removed, or a subinterface or VLAN interface is deleted.

Procedure

1. Enter system view.

system-view

2. Enter IS-IS IPv6 address family view or OSPFv3 process view.

¡ Execute the following commands in sequence to enter IS-IS IPv6 address family view:

isis [ process-id ] [ vpn-instance vpn-instance-name ]

address-family ipv6 [ unicast ]

¡ Enter OSPFv3 process view.

ospfv3 [ process-id | vpn-instance vpn-instance-name ] *

3. Enable dynamic End.X SID deletion delay and set the delay time.

segment-routing ipv6 end-x delete-delay [ time-value ]

By default, dynamic End.X SID deletion delay is enabled and the delay time is 1800 seconds.

Configuring the delay time to flush static End.X SIDs to the FIB

About this task

When a neighbor fails, the interface connected to that neighbor goes down. The End.X SID associated with the interface cannot take effect. When the neighbor recovers, the interface also comes up and the static End.X SID associated with the interface takes effect. Because route convergence has not finished, the local device cannot forward packets according to the route entry of the static End.X SID. As a result, packet forwarding failure or packet loss occurs. (Dynamic End.X SIDs do not have this issue, because they are flushed to the FIB after route convergence is completed.) To avoid this issue, perform this task to delay flushing the static End.X SID associated with the interface to the FIB. During the delay time, the local device does not forward traffic through the link attached to the interface. The delay configuration avoids packet loss within the delay time.

Procedure

1. Enter system view.

system-view

2. Enable SRv6 and enter SRv6 view.

segment-routing ipv6

3. Configure the delay time to flush static End.X SIDs to the FIB

end-x update-delay delay-time

By default, static End.X SIDs are not delayed to flush to the FIB.

Using IGP to advertise SRv6 SIDs

About this task

Use an IGP protocol to advertise a locator and the SRv6 SIDs of that locator by applying the locator to the IGP protocol.

To use an IGP protocol to advertise G-SIDs to neighbors, enable SRv6 compression for that IGP protocol.

Prerequisites

If IS-IS is used to advertise SRv6 SIDs, make sure the cost style of IS-IS is wide, compatible, or wide-compatible. For more information about the cost styles of IS-IS, see Layer 3—IP Routing Configuration Guide.

Using IS-IS to advertise SRv6 SIDs

1. Enter system view.

system-view

2. Enter IS-IS process view.

isis [ process-id ] [ vpn-instance vpn-instance-name ]

3. Enter IS-IS IPv6 address family view.

address-family ipv6 [ unicast ]

4. Apply a locator to IS-IS IPv6 address family.

segment-routing ipv6 locator locator-name [ level-1 | level-2 ] [ auto-sid-coc32 [ additive ] | auto-sid-coc-both { all | coc32 | coc32-all | coc32-none } | auto-sid-disable ][ cost cost-value ] [ tag tag-value ]

By default, no locators are applied to IS-IS IPv6 address family.

Repeat this command to apply multiple locators to IS-IS IPv6 address family for the family to advertise multiple SRv6 SIDs.

5. Enable SRv6 compression for IPv6 IS-IS.

srv6 compress enable [ level-1 | level-2 ]

By default, SRv6 compression is disabled for IPv6 IS-IS.

Use this command only when IPv6 IS-IS is used to advertise G-SIDs.

6. (Optional.) Specify an aggregate route for a locator.

summary ipv6-prefix prefix-length algorithm algo-id [ explicit ]

By default, no aggregate route is specified for a locator.

Use this command to associate routes from a locator with a Flex-Algo algorithm to aggregate the routes. This command reduces the size of the local LSDB and the LSPs generated by the local router.

You can also specify the level-1, level-1-2, and level-2 parameters to aggregate routes in different LSDBs. If you do not specify any of such parameters, the device aggregates only routes in the Level 1 LSDB by default. For more information about route summarization and Flex-Algo algorithms, see IS-IS in Layer 3—IP Routing Configuration Guide.

7. (Optional.) Configure the administrative tag value for SRv6 locators.

segment-routing ipv6 admin-tag tag-value

By default, SRv6 locators do not carry an administrative tag value when they are advertised by IS-IS.

To import only specific SRv6 locators when the device imports IS-IS routes from different levels and areas or learns IS-IS routes from IS-IS neighbors, use this command to configure the administrative tag value for SRv6 locators. Then use the if-match tag command to filter SRv6 locators with different administrative tags.

Using OSPFv3 to advertise SRv6 SIDs

1. Enter system view.

system-view

2. Enter OSPFv3 process view.

ospfv3 [ process-id | vpn-instance vpn-instance-name ] *

3. Apply a locator to the OSPFv3 process.

segment-routing ipv6 locator locator-name[ auto-sid-coc32 [ additive ] | auto-sid-coc-both { all | coc32 | coc32-all | coc32-none } | auto-sid-disable ]

By default, no locators are applied to an OSPFv3 process.

Repeat this command to apply multiple locators to the OSPFv3 process for the process to advertise multiple SRv6 SIDs.

4. Enable SRv6 compression for OSPFv3.

srv6 compress enable

By default, SRv6 compression is disabled for OSPFv3.

Use this command only when OSPFv3 is used to advertise G-SIDs.

5. (Optional.) Specify a type value for an SRv6 SID sub-TLV included in OSPFv3 routes.

segment-routing ipv6 sid-sub-tlv-type { end-x end-x-value | lan-end-x lan-end-x-value }

By default, the type value is 31 for the P2P End.X SID sub-TLV included in OSPFv3 routes and 32 for the LAN End.X SID sub-TLV included in OSPFv3 routes.

The type values for the End.X SID sub-TLVs included in OSPFv3 routes might vary by device model. For device intercommunication, use this command to ensure that all devices have the same type value for the same End.X SID sub-TLV included in OSPFv3 routes.

By default, the type value is 11 for both the P2P End.X SID sub-TLV and ASLA sub-TLV. To avoid conflict, you must use this command to change the type value of the P2P End.X SID sub-TLV.

6. (Optional.) Configure the TLVs and flag bits in the OSPFv3 extensions for SRv6 to be compatible with the private protocol.

segment-routing ipv6 private-srv6-extensions compatible

By default, the SRv6 Capabilities TLV type values, Sub TLV type values, and flag bits in OSPFv3 packets follow the definitions in draft-ietf-lsr-ospfv3-srv6-extensions-09. For a successful advertisement of SRv6 locators and SRv6 SIDs, make sure OSPFv3 neighbors follow the same standard.

If you configure both the segment-routing ipv6 sid-sub-tlv-type and segment-routing ipv6 private-srv6-extensions compatible commands, the End.X SID Sub-TLV Type and LAN End.X SID Sub-TLV Type values specified in the segment-routing ipv6 sid-sub-tlv-type command take precedence.

7. (Optional.) Enable compatibility of the Locator field in SRv6 Locator TLVs with earlier drafts.

segment-routing ipv6 compatible locator-fixed-length

By default, the Locator field in SRv6 locator LSAs is of variable length, with a maximum of 128 bytes.

The length of the Locator field in SRv6 Locator TLVs is defined as variable in draft-ietf-lsr-ospfv3-srv6-extensions-12 and later drafts and can be up to 128 bits. The length of the Locator field can vary based on the configured locator segment length. However, the length is fixed at 128 bits in draft-ietf-lsr-ospfv3-srv6-extensions-11 and earlier drafts.

Enabling BGP to advertise routes for a locator

About this task

Perform this task in an inter-AS BGP network. This task enables the device to generate routes for a locator in the BGP IPv6 unicast routing table and use BGP to advertise the routes to BGP peers.

Procedure

1. Enter system view.

system-view

2. Enter BGP instance view.

bgp as-number [ instance instance-name ]

3. Enter BGP IPv6 unicast address family view.

address-family ipv6 [ unicast ]

4. Configure the device to generate routes for the specified locator in the BGP IPv6 unicast routing table and advertise the routes to BGP peers.

advertise srv6 locator locator-name [ route-policy route-policy-name ]

By default, the device does not generate routes for a locator in the BGP IPv6 unicast routing table.

Configuring dynamic SID deletion delay

About this task

To make sure BGP allocates the same SRv6 SID before and after a BGP session down-up event, use this command to set a proper dynamic SID deletion delay.

With this feature configured, the device does not delete the BGP-allocated SRv6 SID when the BGP session is down before the delay timer expires.

· If the BGP session becomes up before the delay timer expires, the original SRv6 SID is used.

· If the BGP session is down after the delay timer expires, the BGP-allocated SRv6 SID is deleted.

Restrictions and guidelines

If an active/standby MPU switchover occurs before the delay timer expires, the device does not delete the dynamically allocated SRv6 SIDs when the neighbors are disconnected and deletes them until after the timer expires.

If you delete the BGP configuration actively, the device immediately deletes the SRv6 SIDs dynamically allocated by BGP without a delay.

Procedure

1. Enter system view.

system-view

2. Enter BGP instance view.

bgp as-number [ instance instance-name ]

3. Configure the dynamic SID deletion delay time.

segment-routing ipv6 sid delete-delay [ time-value ]

By default, dynamic SID deletion delay time is 1800 seconds.

Configuring the BGP virtual link feature

About this task

BGP EPE uses loopback interfaces to establish an EBGP session to an indirectly connected peer over multiple hops, which might correspond to multiple physical links. In this case, the local address in the link information reported to the controller via BGP-LS by the two indirectly connected BGP EPE peers is the loopback interface address, and the remote address is the next hop address of the direct link. The remote addresses of the two indirectly connected BGP EPE peers do not belong to the same network segment, which means the remote addresses in the BGP EPE peer link information do not match. Therefore, the controller cannot obtain complete inter-AS link topology information based on the link information reported by BGP-LS. It cannot calculate the optimal inter-AS SRv6 TE Policy primary and backup paths based on inter-AS link attributes. Enabling the BGP virtual link feature on indirectly connected BGP EPE peers can resolve such an issue.

You enable this feature on two indirectly connected BGP EPE peers. BGP-LS will use the IPv6 address of the BGP EPE peer specified by the peer egress-engineering srv6 command as the remote BGP neighbor address in the link information reported to the controller. It will the IPv6 address of the local source interface specified by the peer connect-interface command as the local address. Because the local and remote BGP peer addresses in the link information reported by the two non-directly connected BGP EPE peers match, the controller can create a reachable virtual link that does not exist in the actual topology.

You can configure TE metric, affinity attribute, SRLG, and link delay information for a BGP virtual link. For more information, see "Configuring MPLS TE" in MPLS Configuration Guide.

You can bind a BGP virtual link to a TWAMP Light test session. The TWAMP Light test session monitors the network quality of the BGP virtual link and obtains the link delay and jitter. The source IP address in the TWAMP Light test session bound to the BGP virtual link must be consistent with the local IP address of the BGP virtual link. The destination IP address in the TWAMP Light test session must be consistent with the remote IP address of the BGP virtual link. For more information about TWAMP Light test sessions, see "Configuring NQA" in Network Management and Monitoring Configuration Guide.

Restrictions and guidelines

Directly connected BGP EPE peers do not support the BGP virtual link feature or the link attributes configured for the virtual link.

Procedure

1. Enter system view.

system-view

2. Enter BGP instance view.

bgp as-number [ instance instance-name ]

3. Enable the BGP virtual link feature.

peer ipv6-address virtual-link

By default, the BGP virtual link feature is enabled.

4. Specify the TE metric for a BGP virtual link.

peer ipv6-address virtual-link te metric value

By default, a BGP virtual link does not have a TE metric.

5. Add a BGP virtual link to SRLGs.

peer ipv6-address virtual-link te srlg srlg-list

By default, a BGP virtual link does not belong to any SRLG.

6. Specify the affinity attribute value for a BGP virtual link.

peer ipv6-address virtual-link te link administrative group attribute-value

By default, the affinity attribute value for a BGP virtual link is 0x00000000.

7. Bind a BGP virtual link to a TWAMP Light test session.

peer ipv6-address virtual-link twamp-light test-session session-id

By default, a BGP virtual link is not bound to any TWAMP Light test session.

You can bind a BGP virtual link to a TWAMP Light test session. The TWAMP Light test session monitors the network quality of the BGP virtual link and obtains the link delay and jitter. The source IP address in the TWAMP Light test session bound to a BGP virtual link must be consistent with the local IP address of the BGP virtual link. The destination IP address in the TWAMP Light test session must be consistent with the remote IP address of the BGP virtual link.

8. Configure link delay parameters for a BGP virtual link.

peer ipv6-address virtual-link link-delay { average average-delay-value | min min-delay-value max max-delay-value | variation variation-value } *

By default, no link delay parameters are configured for a BGP virtual link.

If you have obtained a link delay parameter by using both this command and dynamic acquisition, the configuration in this command takes effect.

Configuring TI-LFA FRR

Restrictions and guidelines for TI-LFA FRR

By default, no backup path can be calculated by TI-LFA FRR if the next hops of equal-cost primary paths on the source node are different. To address this issue, you can add all equal-cost primary paths on the source node to the same SRLG.

As shown in Figure 18, three equivalent paths Link 1, Link 2, and Link 3 are available from source node Device A to destination node Device E, with their next hops different. For TI-LFA FRR to calculate backup paths, you must add Link 1, Link 2, and Link 3 to the same SRLG.

Figure 18 Using TI-LFA FRR to calculate backup paths in the IS-IS ECMP scenario

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TI-LFA FRR tasks at a glance

To configure TI-LFA FRR, perform the following tasks:

1. Enabling TI-LFA FRR

2. (Optional.) Disabling an interface from participating in TI-LFA calculation

On the source node, disable TI-LFA on the route's output interface to the next hop on the primary path.

3. (Optional.) Enabling FRR microloop avoidance

4. (Optional.) Configuring SR microloop avoidance

¡ Enabling SR microloop avoidance

¡ Configuring SR microloop avoidance to encapsulate only strict SIDs in the SID list

Enabling TI-LFA FRR

Enabling IPv6 IS-IS TI-LFA FRR

1. Enter system view.

system-view

2. Enter IS-IS view.

isis process-id

3. Enter IS-IS IPv6 unicast address family view.

address-family ipv6

4. Enable LFA FRR for IPv6 IS-IS.

fast-reroute lfa [ level-1 | level-2 ]

By default, LFA FRR is disabled for IPv6 IS-IS.

5. Enable TI-LFA FRR for IPv6 IS-IS.

fast-reroute ti-lfa [ per-prefix ] [ route-policy route-policy-name | host ] [ level-1 | level-2 ]

By default, TI-LFA FRR is disabled for IPv6 IS-IS.

6. (Optional.) Set the priority for an FRR backup path selection policy.

fast-reroute tiebreaker { lowest-cost | node-protecting | srlg-disjoint } preference preference [ level-1 | level-2 ]

By default, the priority values of the lowest-cost, node-protection, and SRLG-disjoint backup path selection policies are 20, 40, and 10, respectively.

7. (Optional.) Enable Level-1 TI-LFA to use a Level-2 path as the backup path.

inter-level-tilfa level-1 enable [ prefer ]

By default, Level-1 TI-LFA cannot use a Level-2 path as the backup path.

For more information about this command, see Layer 3—IP Routing Command Reference.

Enabling OSPFv3 TI-LFA FRR

1. Enter system view.

system-view

2. Enter OSPFv3 view.

ospfv3 [ process-id | vpn-instance vpn-instance-name ] *

3. Enable LFA FRR for OSPFv3.

fast-reroute { lfa [ abr-only ] | route-policy route-policy-name }

By default, LFA FRR is disabled for OSPFv3.

4. Enable TI-LFA FRR for OSPFv3.

fast-reroute ti-lfa [ per-prefix ] [ route-policy route-policy-name | host ]

By default, TI-LFA FRR is disabled for OSPFv3.

5. (Optional.) Set the priority for FRR backup path selection policies.

fast-reroute tiebreaker { lowest-cost | node-protecting } preference preference

By default, the priority values of the lowest-cost and node-protection backup path selection policies are 20 and 40, respectively.

Disabling an interface from participating in TI-LFA calculation

Disabling an IPv6 IS-IS interface from participating in TI-LFA calculation

1. Enter system view.

system-view

2. Enter the view of IPv6 IS-IS interface.

interface interface-type interface-number

3. Disable the interface from participating in TI-LFA calculation.

isis ipv6 fast-reroute ti-lfa disable [ level-1 | level-2 ]

By default, an IPv6 IS-IS interface participates in TI-LFA calculation.

Disabling an OSPFv3 interface from participating in TI-LFA calculation

1. Enter system view.

system-view

2. Enter the view of OSPFv3 interface.

interface interface-type interface-number

3. Disable the interface from participating in TI-LFA calculation.

ospfv3 fast-reroute ti-lfa disable [ instance instance-id ]

By default, an OSPFv3 interface participates in TI-LFA calculation.

Enabling FRR microloop avoidance

About this task

FRR microloop avoidance provides microloop avoidance after a network failure.

On a network deployed with TI-LFA FRR, when a node or link fails, traffic will be switched to the backup path calculated by TI-LFA. If devices on the backup path have not finished route convergence, a loop is formed between the source node (failed node or the previous node along the link) and a device on the backup path. The loop exists until the devices on the backup path finish route convergence.

To resolve this issue, configure this feature on a node enabled with TI-LFA FRR. FRR microloop avoidance first switches traffic to the backup path calculated by TI-LFA to avoid packet loss after a node or link failure on the optimal path. Then, that node starts an FRR microloop avoidance RIB-update-delay timer configured by the fast-reroute microloop-avoidance rib-update-delay command after it finishes route convergence. The node performs the following operations only after all nodes on the backup path finish route convergence and the timer times out:

· Issues the forwarding path after route convergence to the FIB.

· Switches traffic from the backup path calculated by TI-LFA to the forwarding path after route convergence.

Restrictions and guidelines

If you configure both FRR microloop avoidance and SR microloop avoidance, FRR microloop avoidance takes precedence over SR microloop avoidance. The FRR microloop avoidance RIB-update-delay timer and SR microloop avoidance RIB-update-delay timer are started for the two features, respectively. The following situations exist depending on the configuration of the two timers:

· If the FRR microloop avoidance RIB-update-delay timer is equal to or greater than the SR microloop avoidance RIB-update-delay timer, traffic is switched to the post-convergence path immediately when the former timer times out.

· If the FRR microloop avoidance RIB-update-delay timer is smaller than the SR microloop avoidance RIB-update-delay timer, traffic is switched to the post-convergence path until after the latter timer times out.

Configuring IPv6 IS-IS FRR microloop avoidance

1. Enter system view.

system-view

2. Enter IS-IS view.

isis process-id

3. Enter IS-IS IPv6 unicast address family view.

address-family ipv6

4. Enable FRR microloop avoidance for IS-IS.

fast-reroute microloop-avoidance enable [ level-1 | level-2 ]

By default, FRR microloop avoidance is disabled for IS-IS.

5. (Optional.) Set the FRR microloop avoidance RIB-update-delay time.

fast-reroute microloop-avoidance rib-update-delay delay-time [ level-1 | level-2 ]

By default, the FRR microloop avoidance RIB-update-delay time is 5000 ms.

Configuring OSPFv3 FRR microloop avoidance

1. Enter system view.

system-view

2. Enter OSPFv3 view.

ospfv3 [ process-id | vpn-instance vpn-instance-name ] *

3. Enable FRR microloop avoidance for OSPFv3.

fast-reroute microloop-avoidance enable

By default, FRR microloop avoidance is disabled for OSPFv3.

4. (Optional.) Set the FRR microloop avoidance RIB-update-delay time.

fast-reroute microloop-avoidance rib-update-delay delay-time

By default, the FRR microloop avoidance RIB-update-delay time is 5000 ms.

Enabling SR microloop avoidance

About this task

SR microloop avoidance provides microloop avoidance after both a network failure and a failure recovery.

After a network failure occurs or recovers, route convergence occurs on relevant network devices. Because of nonsimultaneous convergence on network devices, microloops might be formed. After you configure SR microloop avoidance, the devices will forward traffic along the specified path before route convergence is finished on all the relevant network devices. Because the forwarding path is independent of route convergence, microloops are avoided.

Microloop avoidance after a network failure and a failure recovery is as follows:

· When a network failure occurs, a node enabled with this feature issues the calculated forwarding path to the FIB after route convergence and switches the traffic to the forwarding path after the delay timer times out. Before the timer times out, traffic is forwarded along the TI-LFA FRR backup path to avoid microloops.

· When the failure recovers, a node enabled with this feature also calculates an explicit path that contains SIDs except for the primary forwarding path. Before the timer times out, traffic is forwarded along the backup path to avoid microloops.

To ensure sufficient time for IGP to complete route convergence, set the SR microloop avoidance RIB-update-delay time. Before the timer expires, faulty relevant devices will forward traffic along the specified path. Upon expiration of the timer and completion of IGP route convergence, traffic will traverse along the IGP-calculated path.

Restrictions and guidelines

Configuring IPv6 IS-IS SR microloop avoidance

1. Enter system view.

system-view

2. Enter IS-IS view.

isis process-id

3. Enter IS-IS IPv6 unicast address family view.

address-family ipv6

4. Enable SR microloop avoidance for IPv6 IS-IS.

segment-routing microloop-avoidance enable [ level-1 | level-2 ]

By default, SR microloop avoidance is disabled for IPv6 IS-IS.

5. (Optional.) Set the SR microloop avoidance RIB-update-delay time.

segment-routing microloop-avoidance rib-update-delay delay-time [ level-1 | level-2 ]

By default, the SR microloop avoidance RIB-update-delay time is 5000 ms.

Configuring OSPFv3 SR microloop avoidance

1. Enter system view.

system-view

2. Enter OSPFv3 process view.

ospfv3 [ process-id | vpn-instance vpn-instance-name ] *

3. Enable SR microloop avoidance for OSPFv3.

segment-routing microloop-avoidance enable

By default, SR microloop avoidance is disabled for OSPFv3.

4. (Optional.) Set the SR microloop avoidance RIB-update-delay time.

segment-routing microloop-avoidance rib-update-delay delay-time

By default, the SR microloop avoidance RIB-update-delay time is 5000 ms.

Configuring SR microloop avoidance to encapsulate only strict SIDs in the SID list

About this task

By default, SR microloop avoidance first calculates the End SID to the P node, and then calculates the End.X SIDs from the P node to the destination node. Then, the SIDs are encapsulated into the SRH in the order of the End SID of the P node and the End.X SIDs from the P node to the destination node.

If multipoint failure exists and the forwarding path is frequently switched, a microloop might exist on the path to the P node identified by the End SID. To resolve this issue, use this feature to strictly constrain the path to the P node.

This feature strictly constrains the path to the P node by calculating an End.X SID to reach the P node. The SIDs are encapsulated into the SID list of the SRH in the order of the End.X SID to the P node and the End.X SIDs from the P node to the destination node.

Procedure

1. Enter system view.

system-view

2. Enter IS-IS view.

isis process-id

3. Enter IS-IS IPv6 unicast address family view.

address-family ipv6

4. Configure SR microloop avoidance to encapsulate only strict SIDs in the SID list.

segment-routing microloop-avoidance strict-sid-only

By default, the strict-SID-only feature is not configured for SR microloop avoidance.

Configuring the SRv6 MTU

About this task

Perform this task to configure one of the following MTUs:

· Path MTU—The maximum IPv6 MTU along the path from the source node to the destination node. The transit nodes do not fragment SRv6 tunneled packets. If a packet is larger than the MTU of the output interface, the packet will be discarded. If the MTU is too small, the bandwidth is not sufficiently used. To address these issues, configure an appropriate SRv6 path MTU.

· Reserved MTU—Reserved MTU on the source node for TI-LFA. When packets are switched to the backup path after the primary path fails, the device reconstructs an IPv6 header and SRH for the packets. As a result, packet drop might occur because the packet size has exceeded the MTU. To resolve this issue, configure a reserved MTU on the source node to reserve bytes for adding a new SRH to SRv6 packets in case of primary path failure.

The size of SRv6 packets sent from the source node is controlled by the SRv6 path MTU, reserved MTU, and the IPv6 MTU of the physical output interface. The source node first finds the smaller value between the SRv6 path MTU and the IPv6 MTU of the physical output interface. Then, it uses the smaller value minus the reserved MTU as the effective MTU of the SRv6 packets.

For example, the SRv6 path MTU is 1600 and the reserved MTU is 100.

· If the IPv6 MTU of the physical output interface is equal to or greater then 1600, the effective MTU is the SRv6 path MTU minus the reserved MTU. In this example, the effective MTU is 1500.

· If the IPv6 MTU of the physical output interface is smaller than 1600, the effective MTU is the IPv6 MTU of the physical output interface minus the reserved MTU. For example, if the IPv6 MTU of the physical output interface is 1500, the effective MTU is 1400.

Restrictions and guidelines

Make sure the active MTU is equal to or greater than 1280 bytes.

Procedure

1. Enter system view.

system-view

2. Enter SRv6 view.

segment-routing ipv6

3. Specify a reserved MTU for SRv6 path MTU.

path-mtu reserved [ reserved-value ]

By default, no reserved MTU is specified for SRv6 path MTU.

4. Configure the SRv6 path MTU.

path-mtu mtu-value

The default SRv6 path MTU is 9600 bytes.

Enabling SNMP notifications for SRv6

About this task

Use this feature to report critical SRv6 events to an NMS. For SRv6 event notifications to be sent correctly, you must also configure SNMP on the device. For more information about SNMP configuration, see Network Management and Monitoring Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enable SNMP notifications for SRv6.

snmp-agent trap enable srv6

By default, SNMP notifications are disabled for SRv6.

Display and maintenance commands for SRv6

Execute display commands in any view.

Task	Command
Display IS-IS SRv6 capability information.	display isis segment-routing ipv6 capability [ level-1 \| level-2 ] [ process-id ]
Display IS-IS SRv6 locator routing information.	display isis segment-routing ipv6 locator [ ipv6-address prefix-length ] [ flex-algo flex-algo-id \| [ level-1 \| level-2 ] \| verbose ] * [ process-id ]
Display OSPFv3 SRv6 capability information.	display ospfv3 [ process-id ] segment-routing ipv6 capability
Display OSPFv3 SRv6 locator information.	display ospfv3 [ process-id ] [ flex-algo flex-algo-id ] segment-routing ipv6 locator [ ipv6-address prefix-length ]
Display available static SRv6 SIDs in a locator.	display segment-routing ipv6 available-static-sid locator locator-name [ from begin-value ]
Display brief SRv6 information.	display segment-routing ipv6 brief
Display SRv6 forwarding entries.	display segment-routing ipv6 forwarding [ entry-id [ relation ] \| forwarding-type { srv6be \| srv6frr \| srv6pcpath \| srv6pgroup \| srv6policy \| srv6sfc \| srv6sidlist \| srv6sids } ] [ slot slot-number ]
Display information about the SRv6 local SID forwarding table.	display segment-routing ipv6 local-sid [ locator locator-name ] [ end \| end-am \| end-as \| end-b6encaps \| end-b6encapsred \| end-b6insert \| end-b6insertred \| end-bier \| end-coc-none \| end-coc32 \| end-dt2m \| end-dt2u \| end-dt2ul \| end-dx2 \| end-dx2l \| end-op \| end-rgb ] [ owner owner ] [ sid ] display segment-routing ipv6 local-sid [ locator locator-name ] [ end-dt4 \| end-dt46 \| end-dt6 \| src-dt4 \| src-dt6 ] [ [ owner owner ] sid \| vpn-instance vpn-instance-name ] display segment-routing ipv6 local-sid [ locator locator-name ] [ end-x \| end-x-coc32 \| end-x-coc-none ] [ sid \| interface interface-type interface-number [ nexthop nexthop-ipv6-address ] ] [ owner owner ]
Display statistics about SRv6 SIDs allocated for each protocol.	display segment-routing ipv6 local-sid statistics [ locator [ locator-name ] ]
Display SRv6 locator information.	display segment-routing ipv6 locator [ locator-name ]
Display SRv6 locator configuration and statistics about allocated SRv6 SIDs in locators.	display segment-routing ipv6 locator-statistics [ locator-name ]
Display remote SRv6 SID information.	display segment-routing ipv6 remote-sid { end-dx2 \| end-dx2l } [ sid ]

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SRv6 configuration examples

Example: Configuring IPv6 IS-IS TI-LFA FRR

Network configuration

As shown in Figure 19, complete the following tasks to implement TI-LFA FRR:

· Configure IPv6 IS-IS on Device A, Device B, Device C, and Device D to achieve network level connectivity.

· Configure IS-IS SRv6 on Device A, Device B, Device C, and Device D.

· Configure TI-LFA FRR to remove the loop on Link B and to implement fast traffic switchover to Link B when Link A fails.

Figure 19 Network diagram

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Table 1 Interface and IP address assignment

Device	Interface	IP address	Device	Interface	IP address
Device A	Loop1	1::1/128	Device B	Loop1	2::2/128
	XGE2/0/0	2000:1::1/64		XGE2/0/0	2000:1::2/64
	XGE2/0/1	2000:4::1/64		XGE2/0/1	2000:2::2/64
Device C	Loop1	3::3/128	Device D	Loop1	4::4/128
	XGE2/0/0	2000:3::3/64		XGE2/0/0	2000:3::4/64
	XGE2/0/1	2000:2::3/64		XGE2/0/1	2000:4::4/64

Procedure

1. Configure IPv6 addresses and prefixes for interfaces. (Details not shown.)

2. Configure Device A:

# Configure IPv6 IS-IS to achieve network level connectivity and set the IS-IS cost style to wide.

<DeviceA> system-view

[DeviceA] isis 1

[DeviceA-isis-1] network-entity 00.0000.0000.0001.00

[DeviceA-isis-1] cost-style wide

[DeviceA-isis-1] address-family ipv6

[DeviceA-isis-1-ipv6] quit

[DeviceA-isis-1] quit

[DeviceA] interface ten-gigabitethernet 2/0/0

[DeviceA-Ten-GigabitEthernet2/0/0] isis ipv6 enable 1

[DeviceA-Ten-GigabitEthernet2/0/0] isis cost 10

[DeviceA-Ten-GigabitEthernet2/0/0] quit

[DeviceA] interface ten-gigabitethernet 2/0/1

[DeviceA-Ten-GigabitEthernet2/0/1] isis ipv6 enable 1

[DeviceA-Ten-GigabitEthernet2/0/1] isis cost 10

[DeviceA-Ten-GigabitEthernet2/0/1] quit

[DeviceA] interface loopback 1

[DeviceA-LoopBack1] isis ipv6 enable 1

[DeviceA-LoopBack1] quit

# Enable SRv6 and configure a locator.

[DeviceA] segment-routing ipv6

[DeviceA-segment-routing-ipv6] locator aaa ipv6-prefix 11:: 64 static 32

[DeviceA-segment-routing-ipv6-locator-aaa] quit

[DeviceA-segment-routing-ipv6] quit

# Configure IPv6 IS-IS TI-LFA FRR, and enable SR microloop avoidance.

[DeviceA] isis 1

[DeviceA-isis-1] address-family ipv6

[DeviceA-isis-1-ipv6] fast-reroute lfa

[DeviceA-isis-1-ipv6] fast-reroute ti-lfa

[DeviceA-isis-1-ipv6] fast-reroute microloop-avoidance enable

[DeviceA-isis-1-ipv6] segment-routing microloop-avoidance enable

# Apply the locator to the IPv6 IS-IS process.

[DeviceA-isis-1-ipv6] segment-routing ipv6 locator aaa

[DeviceA-isis-1-ipv6] quit

[DeviceA-isis-1] quit

3. Configure Device B:

# Configure IPv6 IS-IS to achieve network level connectivity and set the IS-IS cost style to wide.

<DeviceB> system-view

[DeviceB] isis 1

[DeviceB-isis-1] network-entity 00.0000.0000.0002.00

[DeviceB-isis-1] cost-style wide

[DeviceB-isis-1] address-family ipv6

[DeviceB-isis-1-ipv6] quit

[DeviceB-isis-1] quit

[DeviceB] interface ten-gigabitethernet 2/0/0

[DeviceB-Ten-GigabitEthernet2/0/0] isis ipv6 enable 1

[DeviceB-Ten-GigabitEthernet2/0/0] isis cost 10

[DeviceB-Ten-GigabitEthernet2/0/0] quit

[DeviceB] interface ten-gigabitethernet 2/0/1

[DeviceB-Ten-GigabitEthernet2/0/1] isis ipv6 enable 1

[DeviceB-Ten-GigabitEthernet2/0/1] isis cost 10

[DeviceB-Ten-GigabitEthernet2/0/1] quit

[DeviceB] interface loopback 1

[DeviceB-LoopBack1] isis ipv6 enable 1

[DeviceB-LoopBack1] quit

# Enable SRv6 and configure a locator.

[DeviceB] segment-routing ipv6

[DeviceB-segment-routing-ipv6] locator bbb ipv6-prefix 22:: 64 static 32

[DeviceB-segment-routing-ipv6-locator-bbb] quit

[DeviceB-segment-routing-ipv6] quit

# Configure IPv6 IS-IS TI-LFA FRR.

[DeviceB] isis 1

[DeviceB-isis-1] address-family ipv6

[DeviceB-isis-1-ipv6] fast-reroute lfa

[DeviceB-isis-1-ipv6] fast-reroute ti-lfa

# Apply the locator to the IPv6 IS-IS process.

[DeviceB-isis-1-ipv6] segment-routing ipv6 locator bbb

[DeviceB-isis-1-ipv6] quit

[DeviceB-isis-1] quit

4. Configure Device C:

# Configure IPv6 IS-IS to achieve network level connectivity and set the IS-IS cost style to wide.

<DeviceC> system-view

[DeviceC] isis 1

[DeviceC-isis-1] network-entity 00.0000.0000.0003.00

[DeviceC-isis-1] cost-style wide

[DeviceC-isis-1] address-family ipv6

[DeviceC-isis-1-ipv6] quit

[DeviceC-isis-1] quit

[DeviceC] interface ten-gigabitethernet 2/0/0

[DeviceC-Ten-GigabitEthernet2/0/0] isis ipv6 enable 1

[DeviceC-Ten-GigabitEthernet2/0/0] isis cost 100

[DeviceC-Ten-GigabitEthernet2/0/0] quit

[DeviceC] interface ten-gigabitethernet 2/0/1

[DeviceC-Ten-GigabitEthernet2/0/1] isis ipv6 enable 1

[DeviceC-Ten-GigabitEthernet2/0/1] isis cost 10

[DeviceC-Ten-GigabitEthernet2/0/1] quit

[DeviceC] interface loopback 1

[DeviceC-LoopBack1] isis ipv6 enable 1

[DeviceC-LoopBack1] quit

# Enable SRv6 and configure a locator.

[DeviceC] segment-routing ipv6

[DeviceC-segment-routing-ipv6] locator ccc ipv6-prefix 33:: 64 static 32

[DeviceC-segment-routing-ipv6-locator-ccc] quit

[DeviceC-segment-routing-ipv6] quit

# Configure IPv6 IS-IS TI-LFA FRR.

[DeviceC] isis 1

[DeviceC-isis-1] address-family ipv6

[DeviceC-isis-1-ipv6] fast-reroute lfa

[DeviceC-isis-1-ipv6] fast-reroute ti-lfa

# Apply the locator to the IPv6 IS-IS process.

[DeviceC-isis-1-ipv6] segment-routing ipv6 locator ccc

[DeviceC-isis-1-ipv6] quit

[DeviceC-isis-1] quit

5. Configure Device D:

# Configure IPv6 IS-IS to achieve network level connectivity and set the IS-IS cost style to wide.

<DeviceD> system-view

[DeviceD] isis 1

[DeviceD-isis-1] network-entity 00.0000.0000.0004.00

[DeviceD-isis-1] cost-style wide

[DeviceD-isis-1] address-family ipv6

[DeviceD-isis-1-ipv6] quit

[DeviceD-isis-1] quit

[DeviceD] interface ten-gigabitethernet 2/0/0

[DeviceD-Ten-GigabitEthernet2/0/0] isis ipv6 enable 1

[DeviceD-Ten-GigabitEthernet2/0/0] isis cost 100

[DeviceD-Ten-GigabitEthernet2/0/0] quit

[DeviceD] interface ten-gigabitethernet 2/0/1

[DeviceD-Ten-GigabitEthernet2/0/1] isis ipv6 enable 1

[DeviceD-Ten-GigabitEthernet2/0/1] isis cost 10

[DeviceD-Ten-GigabitEthernet2/0/1] quit

[DeviceD] interface loopback 1

[DeviceD-LoopBack1] isis ipv6 enable 1

[DeviceD-LoopBack1] quit

# Enable SRv6 and configure a locator.

[DeviceD] segment-routing ipv6

[DeviceD-segment-routing-ipv6] locator ddd ipv6-prefix 44:: 64 static 32

[DeviceD-segment-routing-ipv6-locator-ddd] quit

[DeviceD-segment-routing-ipv6] quit

# Configure IPv6 IS-IS TI-LFA FRR.

[DeviceD] isis 1

[DeviceD-isis-1] address-family ipv6

[DeviceD-isis-1-ipv6] fast-reroute lfa

[DeviceD-isis-1-ipv6] fast-reroute ti-lfa

# Apply the locator to the IPv6 IS-IS process.

[DeviceD-isis-1-ipv6] segment-routing ipv6 locator ddd

[DeviceD-isis-1-ipv6] quit

[DeviceD-isis-1] quit

Verifying the configuration

# Display IPv6 IS-IS routing information for 3::3/128.

[DeviceA] display isis route ipv6 3::3 128 verbose

Route information for IS-IS(1)

------------------------------

Level-1 IPv6 forwarding table

-----------------------------

IPv6 dest : 3::3/128

Flag : R/L/- Cost : 20

Admin tag : - Src count : 2

Nexthop : FE80::4449:7CFF:FEE0:206

NexthopFlag : -

Interface : XGE2/0/0

TI-LFA:

Interface : XGE2/0/1

BkNextHop : FE80::4449:91FF:FE42:407

LsIndex : 0x80000001

Backup label stack(top->bottom): {44::1:0:1}

Nib ID : 0x24000006

Flags: D-Direct, R-Added to Rib, L-Advertised in LSPs, U-Up/Down Bit Set

The output shows TI-LFA backup next hop information.

08-Segment Routing Configuration Guide

Basic concepts

SR node roles

SID portions

SRv6 endpoint behaviors

SRv6 SID flavors

Local SID forwarding table

Segment List

SRv6 tunnel

SRv6 packet forwarding

Static routing

Automatic route advertisement

G-SRv6 packet format

Calculating the destination address with G-SID

TI-LFA FRR background

TI-LFA FRR concepts

Protocols and standards

Prerequisites for SRv6

Configuring non-compressible SRv6 SIDs

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Procedure

About this task

Prerequisites

Using IS-IS to advertise SRv6 SIDs

Using OSPFv3 to advertise SRv6 SIDs

About this task

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure

Configuring TI-LFA FRR

Enabling IPv6 IS-IS TI-LFA FRR

Disabling an IPv6 IS-IS interface from participating in TI-LFA calculation

About this task

Restrictions and guidelines

Configuring IPv6 IS-IS FRR microloop avoidance

Configuring OSPFv3 FRR microloop avoidance

About this task

Restrictions and guidelines

Configuring IPv6 IS-IS SR microloop avoidance

Configuring OSPFv3 SR microloop avoidance

About this task

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Procedure

Display and maintenance commands for SRv6

Network configuration

Procedure

Verifying the configuration

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