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

Basic concepts

SR node

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

· Ingress node (source node)—Selects a path for packet forwarding, encodes the path as an ordered SID list in the routing extension header.

· Transit node—Forwards the packets based on the SID list.

· Egress node (tail node)—Removes the routing extension header and forwards the packets to the destination.

SID

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. 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. An SR node will execute the function in the SRv6 SID Function field of an SRv6 packet after it receives that SRv6 packet.

· Arguments—Defines flow and service parameters for SRv6 packets.

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

Figure 1 SRv6 SID

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According to whether SRv6 SIDs are compressible, SRv6 SIDs are divided into the following categories for a locator:

· Non-compressible SRv6 SIDs—Include static and dynamic SRv6 SIDs. The formats are as follows:

¡ Static SRv6 SID = ipv6-prefix + 0s + opcode + 0s.

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

- The number of bits occupied by 0s (following the ipv6-prefix portion) is determined by the dynamic-length argument.

- The opcode portion is specified by using the opcode command. The number of bits occupied by the opcode portion is determined by the static-length argument.

- The number of bits occupied by 0s (following the opcode portion) is determined by the args-length argument.

¡ Dynamic SRv6 SID = ipv6-prefix + dynamic + 0s.

- The dynamic portion is dynamically assigned by IGP or BGP. The number of bits occupied by the dynamic portion is determined by the dynamic-length argument.

- The number of bits occupied by 0s is the sum of the values for the static-length and args-length arguments.

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 prefix 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::.

Figure 2 Non-compressible SRv6 SIDs

· Compressible SRv6 SIDs—You can specify compressible SRv6 SIDs in a static segment or use IGP to automatically allocate compressible SRv6 SIDs in a dynamic segment. For example, use the locator test1 ipv6-prefix 100:200:DB8:ABCD:: 64 common-prefix 48 coc32 static 8 args 16 command.

¡ The locator is 100:200:DB8:ABCD::. The prefix 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.

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::.

Figure 3 Compressible SRv6 SIDs

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According to the functions of SRv6 SIDs, SRv6 SIDs are divided into the following categories:

· End SID—Identifies the prefix of a destination address in the network.

· End.X SID—Identifies a link in the network.

· End.DT4 SID—Identifies an IPv4 VPN 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 MPLS L3VPN and EVPN L3VPN scenarios.

· End.DT6 SID—Identifies an IPv6 VPN 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 MPLS L3VPN and IPv6 EVPN L3VPN scenarios.

· End.DT46 SID—Identifies an IPv4 or IPv6 VPN in the network.

· End.DX2 SID—Identifies one end of a Layer 2 cross-connect. The function of an End.DX2 SID is removing the outer IPv6 header and SRH of packets and forwarding the decapsulated packets to the output interface of the SID. End.DX2 SIDs are applicable to EVPN VPWS scenarios.

· 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 and floods traffic. The function of an End.DT2M SID is removing the outer IPv6 header and SRH of packets and flooding the decapsulated packets in the BD. End.DT2M SIDs are applicable to EVPN VPLS BUM traffic.

· 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.M SID—Applies to the SRv6 TE policy tailend protection scenario. For more information about End.M SIDs, see "Configuring SRv6 TE policies."

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

· End.AS SID—Applies to the SRv6 service chain static proxy scenario. For more information about End.AS SIDs, see "Configuring SRv6 service chains."

· End.AM SID—Applies to the SRv6 service chain masquerading scenario. For more information about End.AM SIDs, see "Configuring SRv6 service chains."

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

Use SRv6 SID flavors to change the forwarding behaviors of SRv6 SIDs in order to meet multiple service requirements. The following SRv6 SID flavors are supported:

· 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.

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 4, 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 4 SRv6 packet format

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SRv6 packet forwarding

As shown in Figure 5, an IPv6 packet is forwarded through an SRv6 tunnel as follows:

1. Upon receiving an IPv6 packet, Device A finds in the routing table that the outgoing interface is an SRv6 tunnel interface. The packet is delivered to the tunnel interface.

2. The SRv6 tunnel interface encapsulates the IPv6 packet as follows:

¡ Adds an SRH header. The Segments Left (SL) value is the number of segments minus one. The path from ingress to egress has three segments, so the SL value is set to 2. The encapsulated SID list is Segment List [0]=D, Segment List [1]=C, Segment List [2]=B. The Segment List is encoded starting from the last segment of the path to the first segment of the path.

¡ Adds an outer IPv6 header. The source address is the tunnel source, and the destination address is determined by the SL value. On Device A, the SL value is 2, which points to the IPv6 address of Device B, so the destination address is the IPv6 address of Device B.

3. Device A searches the routing table for the destination address in the newly encapsulated IPv6 header, and forwards the packet to Device B.

4. Device B first checks the destination address and SID type in the outer IPv6 header.

¡ If the SID type is End.X, the device obtains the output interface and next hop information based on the End.X SID.

¡ If the SID is not End.X, the device does not perform any operation.

Then, the device checks the SL value in the SRH header and decreases the value by one. Then, the device searches for the IPv6 address pointed by Segment List [1] and uses the IPv6 address of Device C to replace the destination address of the outer IPv6 header.

5. Device B performs one of the following operations depending on the SID type:

¡ For an End.X SID, the device forwards the encapsulated packet to Device C based on the obtained output interface and next hop information.

¡ For an SID of the other type, the device searches the routing table for the destination address in the outer IPv6 header and forwards the packet to Device C.

6. Device C performs the same operations as what Device B has done in steps 4 and 5, and then forwards the packet to Device D.

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

a. De-encapsulates the packet by removing the outer IPv6 header and the SRH header.

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

Figure 5 SRv6 tunnel 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 6, 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 6 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 7, 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 7 Compressible SRv6 SID

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G-SRv6 packet

G-SRv6 packet format

As shown in Figure 8, 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 8 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 8 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 9, 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 9 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.

BGP-EPE

IGP for SRv6 cannot advertise SRv6 SIDs across ASs. To advertise SRv6 SIDs across ASs, use BGP Egress Peer Engineering (BGP-EPE).

BGP-EPE can allocate BGP peer SIDs to inter-AS segments.

· If the device has established BGP LS peer relationship with a network controller, it advertises the peer SIDs to the network controller through extended BGP LS messages. Then, the controller orchestrates the IGP SIDs and BGP peer SIDs to realize optimal inter-AS traffic forwarding.

· If the device has not established BGP LS peer relationship with a network controller, it advertises the peer SIDs to a BGP peer through BGP LS messages. When a device that has established BGP LS peer relationship with a network controller receives the peer SIDs, it advertises the peer SIDs to the network controller through BGP LS messages.

BGP-EPE supports automatic peer SID allocation and static peer SID allocation. As shown in Figure 10, BGP-EPE can allocate the following peer SIDs:

· PeerNode SID—Identifies a peer node. BGP-EPE allocates a PeerNode SID to each BGP session. If the device establishes EBGP peer relationship with a peer through a loopback interface, it might have multiple physical links to reach the peer. In this case, the PeerNode SID for this peer is associated with multiple output interfaces. Traffic destined for this peer based on the PeerNode SID will be distributed among these output interfaces.

· PeerAdj SID—Identifies an adjacency link that can reach a peer node. If the device establishes EBGP peer relationship with a peer through a loopback interface, it might have multiple physical links to reach the peer. Each link is allocated a PeerAdj SID. When the device forwards traffic based on a PeerAdj SID, the traffic is forwarded out of the interface that is attached to the link identified by the PeerAdj SID.

· PeerNode-Adj SID—Identifies a peer node and identifies one or multiple adjacency links that can reach a peer node.

· PeerSet SID—Identifies a group of peer nodes in a BGP-EPE SRv6 peer set. A PeerSet SID corresponds to multiple PeerNode SIDs and PeerAdj SIDs. When the device forwards traffic based on a PeerSet SID, it distributes the traffic among multiple peers.

Figure 10 BGP-EPE network diagram

As shown in Figure 10, BGP-EPE allocates peer SIDs as follows:

· ASBR 1 and ASBR 3 have two direct physical links. They establish EBGP peer relationship through loopback interfaces. On ASBR 1, BGP-EPE allocates PeerNode SID 100:AB::1 to ASBR 3 and allocates PeerAdj SIDs 100:AB:1::2 and 100:AB:1::3 to the physical links. When ASBR 1 forwards traffic to ASBR 3 based on the PeerNode SID, the two physical links load share the traffic.

· EBGP peer relationship has been established between ASBR 1 and ASBR 5, between ARBR 2 and ASBR 4, and between ASBR 2 and ASBR 5 through directly connected physical interfaces. On ASBR 1, BGP-EPE allocates PeerNode SID 100:AB::2 to ASBR 5. On ASBR 2, BGP-EPE allocates PeerNode SIDs 100:AB::4 and 100:AB::5 to ASBR 4 and ASBR 5, respectively.

· ASBR 4 and ASBR 5 each has established EBGP peer relationship with ASBR 2. On ASBR 2, peers ASBR 4 and ASBR 5 are added to a peer set. BGP-EPE allocates PeerSet SID 100:AB::3 to the peer set. When ASBR 2 forwards traffic based on the PeerSet SID, the traffic is distributed to both ASBR 4 and ASBR 5 for load sharing.

The SIDs allocated to peers by BGP-EPE are not advertised to the peers. Route types used by the peers do not affect BGP-EPE.

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

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

· P space—Use the source node of the protected link as the root to establish a shortest path tree. All nodes that are reachable from the source node without passing the protected link form the P space. Nodes in the P space are called P nodes.

· Extended P space—Use the source node of the protected link and its neighbors as the roots to establish shortest path trees. All nodes that are reachable from the source node or one of its neighbors without passing the protected link form the extended P space. The P space is a subset of the extended P space.

· Q space—Use the destination node of the protected link as the root to establish a reverse shortest path tree. All nodes that are reachable from the root node without passing the protected link form the Q space. Nodes in the Q space are called Q nodes.

· Repair list—A constraint path used to indicate how a P node reaches a Q node when the P space and Q space do not have common nodes. The repair list contains the following SRv6 SIDs:

¡ SRv6 SIDs of P nodes.

¡ SRv6 SIDs from P nodes to nearest Q nodes.

TI-LFA FRR protection types

The following TI-LFA traffic protection types are available:

· Link protection—Protects traffic that traverses a specific link.

· Node protection—Protects traffic that traverses a specific node.

Node protection takes precedence over link protection.

TI-LFA FRR path calculation

As shown in Figure 13, 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 13 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 14, 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 14 Data forwarding over the TI-LFA FRR backup path

SR microloop avoidance after a network failure

As shown in Figure 15, 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.

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 15 Diagram for SR microloop avoidance after a network failure

SR microloop avoidance after a failure recovery

As shown in Figure 16, 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 16 Diagram for SR microloop avoidance after a failure recovery

‌

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 an SRv6 SID

2. Configuring G-SIDs

This task is required if SRv6 compression is enabled.

3. (Optional.) Configuring dynamic End.X SID deletion delay

4. Specifying a source address for the outer IPv6 header of SRv6-encapsulated packets

5. Using IGP to advertise SRv6 SIDs

6. Configuring BGP for SRv6

¡ Enabling BGP to advertise routes for a locator

¡ Configuring BGP-EPE

7. Configuring SRv6 tunneling

Perform the following tasks on the source node of an SRv6 tunnel:

a. Configuring an SID list

b. Specifying an SID list for an SRv6 tunnel

c. (Optional.) Configuring a service class for an SRv6 tunnel

d. (Optional.) Enabling BFD echo-mode detection for an SRv6 tunnel

8. (Optional.) Configuring traffic forwarding

9. (Optional.) Configuring TI-LFA FRR

10. (Optional.) Configuring the SRv6 MTU

11. (Optional.) Configuring the SRv6 DiffServ mode

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 an SRv6 SID

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.

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 End SID.

opcode { opcode | hex hex-opcode } end [ no-psp ]

¡ Configure an End.X SID.

opcode { opcode | hex hex-opcode } end-x interface interface-type interface-number nexthop nexthop-ipv6-address [ no-psp ]

¡ Configure an End.DT4 SID.

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

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

¡ Configure an End.DT6 SID.

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

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

¡ Configure an End.DT46 SID.

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

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

¡ Configure an End.DX4 SID.

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. An End.DX4 SID cannot be configured with different output interfaces or next hops.

¡ Configure an End.DX6 SID.

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. An End.DX6 SID cannot be configured with different output interfaces or next hops.

¡ Configure an End.DX2 SID.

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 End.DX2L SID.

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 End.DT2M SID.

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

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

¡ Configure an End.DT2U SID.

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

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

¡ Configure an End.DT2UL SID.

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

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

¡ Configure an End.M SID.

opcode { opcode | hex hex-opcode } end-m mirror-locator ipv6-address prefix-length

¡ Configure an End.OP SID.

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 [ static static-length ] ]

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

¡ Configure an End SID.

opcode opcode end-coc32 [ no-psp ]

¡ Configure an End.X SID.

opcode opcode end-x-coc32 interface interface-type interface-number nexthop nexthop-address [ no-psp ]

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.

Specifying a source address for the outer IPv6 header of SRv6-encapsulated packets

Restrictions and guidelines

As a best practice to ensure correct traffic forwarding in an SRv6 network, specify a source address for the outer IPv6 header of SRv6-encapsulated packets.

You cannot specify a loopback address, link-local address, multicast address, or unspecified address as the source IPv6 address. You must specify an IPv6 address of the local device as the source IPv6 address, and make sure the IPv6 address has been advertised by a routing protocol. As a best practice, specify a loopback interface address of the local device as the source IPv6 address.

Procedure

1. Enter system view.

system-view

2. Enter SRv6 view.

segment-routing ipv6

3. Specify a source address for the outer IPv6 header of SRv6-encapsulated packets.

encapsulation source-address ipv6-address [ ip-ttl ttl-value ]

By default, no source address is specified for the outer IPv6 header of SRv6-encapsulated packets.

Using IGP to advertise SRv6 SIDs

About this task

Use an IGP protocol to advertise the SRv6 SID of a 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-disable ]

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.

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-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.

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 BGP-EPE

Enabling SRv6 BGP-EPE

About this task

BGP-EPE allocates BGP peer SIDs to inter-AS segments. The device advertises the peer SIDs to a network controller through BGP LS messages. The controller orchestrates the IGP SIDs and BGP peer SIDs to realize optimal inter-AS traffic forwarding.

With this feature, the device can allocate SRv6 SIDs to its connected BGP peers or peer groups to identify its connected BGP peers or links.

Restrictions and guidelines

If you do not specify any parameters for the peer egress-engineering srv6 command, the device will dynamically allocate SRv6 SIDs to peers. The SRv6 SIDs belong to the locator specified by using the segment-routing ipv6 egress-engineering locator command in BGP instance view.

When you use the peer egress-engineering srv6 command for a peer, follow these restrictions and guidelines:

· If you use this command to specify multiple locators for that peer, only the most recent configuration takes effect.

· If you use this command to specify multiple static SRv6 SIDs and the SIDs belong to different types, all types of SRv6 SIDs can take effect. For the same type of SRv6 SIDs, only the most recent configuration takes effect.

If you specify a static SRv6 SID for a peer, the specified static SRv6 SID must belong to the locator specified by using the segment-routing ipv6 egress-engineering locator command in BGP instance view.

The static SRv6 SIDs specified by using the following commands cannot be the same:

· peer egress-engineering srv6.

· egress-engineering srv6 peer-set.

Procedure

1. Enter system view.

system-view

2. Enter BGP instance view.

bgp as-number [ instance instance-name ]

3. Enable SRv6 BGP-EPE.

peer group-name egress-engineering srv6

peer ipv6-address [ prefix-length ] egress-engineering srv6 [ locator locator-name | static-sid { psp psp-sid | no-psp-usp no-psp-usp-sid } * ]

By default, SRv6 BGP-EPE is disabled.

Applying a locator to BGP-EPE

About this task

Perform this task to restrict the range of End.X SIDs that can be allocated to BGP-EPE SRv6 peer sets and BGP-EPE-enabled peers in a BGP instance. All static SRv6 SIDs configured for the BGP-EPE SRv6 peer sets and peers must belong to the locator specified by performing this task.

Restrictions and guidelines

To dynamically allocate End.X SIDs from the specified locator:

· Do not configure a static SRv6 SID when you create a BGP-EPE SRv6 peer set by using the egress-engineering srv6 peer-set command.

· Do not specify a locator or configure a static SRv6 SID when you enable SRv6 BGP-EPE for a peer by using the peer egress-engineering srv6 command.

Procedure

1. Enter system view.

system-view

2. Enter BGP instance view.

bgp as-number [ instance instance-name ]

3. Apply a locator to BGP-EPE.

segment-routing ipv6 egress-engineering locator locator-name

By default, no locator is applied to BGP-EPE.

Configuring a BGP-EPE SRv6 peer set

About this task

If the device establishes BGP peer relationship with multiple devices, perform this task to add the peer devices to a peer set and allocate a PeerSet SID to the peer set. When the device forwards traffic based on the PeerSet SID, it distributes the traffic among the peers for load sharing.

Prerequisites

Enable SRv6 BGP-EPE on all peers that will be added to the BGP-EPE SRv6 peer set.

Use the segment-routing ipv6 egress-engineering locator command in BGP instance view to apply a locator to BGP-EPE.

· If automatic SID allocation is used, the device dynamically allocates an SRv6 SID to the BGP-EPE SRv6 peer set from the specified locator.

· If you specify a static SRv6 SID for the BGP-EPE SRv6 peer set, the specified static SRv6 SID must belong to the specified locator.

If you execute the egress-engineering srv6 peer-set command to specify multiple SRv6 SIDs for one peer set, the effective configuration depends on whether the SRv6 SIDs are the same type.

· If all the SRv6 SIDs belong to the same type, only the most recent configuration takes effect.

· If the SRv6 SIDs belong to different types, the configuration for all the SRv6 SID types takes effect. For the SRv6 SIDs that belong to the same type, only the most recent configuration takes effect. Make sure each SRv6 SID is unique among all the SRv6 SID types.

The static SRv6 SIDs configured by using the following commands cannot be the same:

· egress-engineering srv6 peer-set.

· peer egress-engineering srv6.

Procedure

1. Enter system view.

system-view

2. Enter BGP instance view.

bgp as-number [ instance instance-name ]

3. Create a BGP-EPE SRv6 peer set.

egress-engineering srv6 peer-set peer-set-name [ static-sid { psp psp-sid | no-psp-usp no-psp-usp-sid } * ]

4. Add a peer to the BGP-EPE SRv6 peer set.

peer { ipv6-address [ prefix-length ] } peer-set srv6-peer-set-name

By default, no peers are added to a BGP-EPE SRv6 peer set.

To change the BGP-EPE SRv6 peer set for a peer, you must first use undo peer peer-set command to remove that peer from the original BGP-EPE SRv6 peer set.

Configuring SRv6 tunneling

Configuring an SID list

About this task

An SR node is uniquely identified by an SID index in an SID list. The SID list forms a forwarding path. The SR nodes in the list are arranged by SID index in ascending sort order. When the device encapsulates the Segment List, SRv6 automatically assigns a segment index to each SR node based on their SID indexes. The smallest SID index corresponds to the largest segment index, and the largest SID index corresponds to the smallest segment index.

Restrictions and guidelines

If you do not specify an SID index for an SR node, SRv6 automatically assigns an SID index to the node. The assigned SID index is the largest index that has been assigned plus an increment.

Make sure the node nearest to the source node is assigned the smallest SID index. The nearer a node is to the source node, the smaller the SID index value of the node must be.

After an SID list is applied to an up tunnel, changing the SID list of the tunnel will cause the tunnel to go down. The new SID list cannot take effect until the device finishes route convergence.

Procedure

1. Enter system view.

system-view

2. Create an SID list and enter its view.

ipv6 segment-routing sid-list list-name

3. Configure an SR node in the SID list.

sid [ index index-number ] ipv6-address

To make the node reachable by other nodes, configure IGP on the node to advertise the SRv6 SID of the node.

Specifying an SID list for an SRv6 tunnel

1. Enter system view.

system-view

2. Create an SRv6 tunnel interface and enter its view.

interface tunnel tunnel-number mode sr ipv6

3. Specify an SID list for the tunnel.

tunnel sid-list list-name [ backup ]

By default, no SID lists are specified for an SRv6 tunnel.

Configuring a service class for an SRv6 tunnel

About this task

Class Based Tunnel Selection (CBTS) compares the service class value of the traffic with the service class values of SRv6 tunnels. CBTS uses the following rules to select a tunnel to forward the traffic:

· If the traffic matches an SRv6 tunnel, CBTS uses this tunnel.

· If the traffic matches multiple SRv6 tunnels, CBTS selects a tunnel based on the flow forwarding mode set on the tunnel interface.

¡ If flow-based forwarding is set, CBTS randomly selects a matching tunnel for packets of the same flow.

¡ If packet-based forwarding is set, CBTS uses all matching tunnels to load share the packets.

· If the traffic does not match any SRv6 tunnels, CBTS selects an SRv6 tunnel from all tunnels with a service class value smaller than the traffic. Among these tunnels, the one with the largest service class value is used. If all SRv6 tunnels have a service class value greater than the traffic, CBTS uses the tunnel with the smallest service class value.

Procedure

1. Enter system view.

system-view

2. Enter SRv6 tunnel interface view.

interface tunnel tunnel-number [ mode sr ipv6 ]

3. Configure a service class for the tunnel.

service-class class-value

By default, no service class is configured for an SRv6 tunnel.

Enabling BFD echo-mode detection for an SRv6 tunnel

About this task

Perform this task on an SRv6 tunnel interface to use BFD sessions for quick link connectivity detection of the SRv6 tunnel. If a link failure is detected along the path, the device can quickly handle the issue, for example, it can direct the traffic to the backup path to ensure traffic forwarding continuity.

If the BFD session of a path is down, the path is unavailable. If the BFD session of a path is up, the path is available.

Procedure

1. Enter system view.

system-view

2. Configure the source IPv6 address of BFD echo packets.

bfd echo-source-ipv6 ipv6-address

By default, no source IPv6 address is configured for BFD echo packets.

As a best practice, do not configure the source IPv6 address to be on the same network segment as any local interfaces. If you configure such a source IPv6 address, a large number of ICMPv6 redirect packets might be sent from the peer, resulting in link congestion. For more information about this command, see BFD in High Availability Configuration Guide.

3. Enter SRv6 tunnel interface view.

interface tunnel tunnel-number [ mode sr ipv6 ]

4. Enable BFD echo-mode detection.

tunnel bfd enable echo

By default, BFD echo-mode detection is disabled for an SRv6 tunnel.

Configuring traffic forwarding

Configuring a static route to direct traffic to an SRv6 tunnel

For information about the command to configure a static route, see Layer 3—IP Routing Command Reference. The interface specified in this command must be an SRv6 tunnel interface.

Configuring automatic static route advertisement to direct traffic to an SRv6 tunnel

About this task

Perform this task on an SRv6 tunnel interface to create a static route whose destination address and output interface are the tunnel destination address and the tunnel interface, respectively.

Procedure

1. Enter system view.

system-view

2. Enter SRv6 tunnel interface view.

interface tunnel tunnel-number [ mode sr ipv6 ]

3. Configure automatic static route advertisement.

tunnel route-static [ preference preference-value ]

By default, automatic static route advertisement is not configured.

Configuring automatic IGP route advertisement to direct traffic to an SRv6 tunnel

About this task

To direct traffic to an SRv6 tunnel, you can distribute the SRv6 tunnel to the IGP and make the SRv6 tunnel participate in IGP route calculation. To achieve these purposes, deploy the following functionalities:

· IPv6 router ID.

The IPv6 router ID determines the source and destination addresses of the SRv6 tunnel distributed to the IGP. The destination address of the SRv6 tunnel must be the same as the IPv6 router ID of the destination node.

Configuring an IPv6 route ID on a router also enables the IPv6 TE feature on that router. After the SRv6 tunnel participates in IGP route calculation, traffic can be directed to the SRv6 tunnel.

· Automatic route advertisement.

This functionality distributes the SRv6 tunnel to the IGP and makes the SRv6 tunnel participate in IGP route calculation.

Restrictions and guidelines for directing traffic to an SRv6 tunnel

The IPv6 router ID must be unique in the IPv6 network.

To avoid routing loops in a ring topology when a link on the SRv6 tunnel is down, set the SIDs in the SID list of the SRv6 tunnel to have 128-bit prefixes. IGP does not set the output interface of a host route to the SRv6 tunnel interface.

Prerequisites for directing traffic to an SRv6 tunnel

Before you configure the IPv6 router ID for IS-IS, 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.

Before you configure automatic route advertisement, you must enable IPv6 capability for the IGP protocol on the SRv6 tunnel interface.

Configuring the IPv6 router ID and enabling IPv6 TE

1. Enter system view.

system-view

2. Enter IS-IS view.

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

3. Enter IS-IS IPv6 address family view.

address-family ipv6 [ unicast ]

4. Configure the IPv6 router ID for IS-IS and enable IPv6 TE.

router-id ipv6-address

By default, no IPv6 router ID is configured for IS-IS and IPv6 TE is disabled.

Configuring IGP shortcut

1. Enter system view.

system-view

2. Enter SRv6 tunnel interface view.

interface tunnel tunnel-number mode sr ipv6

3. Enable IGP shortcut.

srv6 igp shortcut [ isis | ospf ]

By default, IGP shortcut is disabled.

Only IS-IS supports IGP shortcut in the current software version.

4. Assign a metric to the SRv6 tunnel.

srv6 igp metric { absolute value | relative value }

By default, the metric of an SRv6 tunnel equals its IGP metric.

Configuring TI-LFA FRR

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.) Configuring FRR microloop avoidance

4. (Optional.) Configuring SR microloop avoidance

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.

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.

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.

Configuring 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 a device along the backup path has not finished route convergence, a traffic loop will occur. Traffic will be looped between the device and the source node (the node prior to the node or link that failed) until the device finishes route convergence.

To resolve this issue, FRR microloop avoidance first switches traffic to the backup path calculated by TI-LFA after the node or link failure. Then, the source node waits for the nodes on the backup path to finish route convergence before starting route convergence.

Restrictions and guidelines

If you configure both FRR microloop avoidance and SR microloop avoidance, SR microloop avoidance takes effect.

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. 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 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.

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.

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 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 reconstrcts 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 SRv6 path MTU minus the reserved MTU is the active MTU. The effective MTU for SRv6 packets on the source node is the smaller value from the following values:

· The active MTU.

· The IPv6 MTU of the physical output interface.

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 setting is 1500 bytes.

Configuring the SRv6 DiffServ mode

About this task

SRv6 DiffServ mode determines how an SRv6 node processes the IP precedence and DSCP for packets forwarded between an IP network and an SRv6 network. The device supports the following SRv6 DiffServ modes:

· Pipe mode—When a packet enters the SRv6 network, the ingress node adds a new IPv6 header to the original packet. The ingress node ignores the IP precedence or DSCP value in the original packet and uses the value specified by using the service-class argument as the traffic class in the new IPv6 header. In the SRv6 network, SRv6 nodes perform QoS scheduling for the packet based on the specified traffic class. When the packet leaves the SRv6 network, the egress node removes the outer IPv6 header from the packet without modifying the IP precedence or DSCP value in the original packet.

· Short-pipe mode—When a packet enters and leaves the SRv6 network, all SRv6 nodes process the packet in the same way as in pipe mode except for the egress node. After the egress node removes the outer IPv6 header from the packet, it performs QoS scheduling as follows:

¡ If no priority trust mode is configured, the egress node performs QoS scheduling for the packet based on the IP precedence or DSCP value in the original packet.

¡ If a priority trust mode is configured, the egress node performs QoS scheduling for the packet based on the trusted priority.

· Uniform mode—When a packet enters the IPv6 network, the ingress node maps the IP precedence or DSCP value in the original IP header to the outer IPv6 header as the traffic class. When the packet leaves the SRv6 network, the egress node maps the traffic class value in the outer IPv6 header to the original packet as the IP precedence or DSCP value.

Restrictions and guidelines

When you configure the SRv6 DiffServ mode on the source and destination nodes of an SRv6 tunnel, follow these restrictions and guidelines:

· The outbound DiffServ mode on the local end must be the same as the inbound DiffServ mode on the peer end.

· The inbound DiffServ mode on the local end must be the same as the outbound DiffServ mode on the peer end.

For more information about IP precedence and DSCP, see priority mapping configuration in QoS Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enter SRv6 view.

segment-routing ipv6

3. Configure the SRv6 DiffServ mode.

diffserv-mode { ingress { pipe service-class | short-pipe service-class | uniform } egress { pipe | short-pipe | uniform } | { pipe service-class | short-pipe service-class | uniform } }

By default, the SRv6 DiffServ mode is uniform.

Verifying and maintaining SRv6

Displaying basic SRv6 configuration information

Perform display tasks in any view.

· Display SRv6 forwarding entries.

display segment-routing ipv6 forwarding [ entry-id ] [ slot slot-number ]

· Display information about the SRv6 local SID forwarding table.

display segment-routing ipv6 local-sid { end | end-am | end-as | end-b6encaps | end-coc32 | end-dt2m | end-dt2u | end-dt2ul | end-dx2 | end-dx2l | end-m | end-op | end-t | end-x-coc32 } [ sid ]

display segment-routing ipv6 local-sid { end-dt4 | end-dt46 | end-dt6 | end-dx4 | end-dx6 } [ sid | vpn-instance vpn-instance-name ]

display segment-routing ipv6 local-sid end-x [ sid | interface interface-type interface-number [ nexthop nexthop-ipv6-address ] ]

· Display SRv6 locator information.

display segment-routing ipv6 locator [ locator-name ]

· Display SID list information.

display ipv6 segment-routing sid-list [ list-name ]

Displaying SRv6 BGP-EPE information

Perform display tasks in any view.

· Display BGP-EPE information for IPv6 peers.

display bgp [ instance instance-name ] egress-engineering ipv6 [ ipv6-address ] [ verbose ]

· Display information about BGP-EPE SRv6 peer sets.

display bgp egress-engineering srv6 peer-set [ srv6-peer-set-name ]

Displaying IS-IS SRv6 information

Perform display tasks in any view.

· 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 ] [ [ level-1 | level-2 ] | verbose ] * [ process-id ]

· Display IS-IS SRv6 tunnel interface information.

display isis srv6 tunnel [ level-1 | level-2 ] [ process-id ]

Displaying OSPFv3 SRv6 information

Perform display tasks in any view.

· Display OSPFv3 SRv6 capability information.

display ospfv3 [ process-id ] segment-routing ipv6 capability

· Display OSPFv3 SRv6 locator information.

display ospfv3 [ process-id ] segment-routing ipv6 locator [ ipv6-address prefix-length ]

· Display OSPFv3 SRv6 tunnel interface information.

display ospfv3 [ process-id ] srv6 tunnel [ interface-number ]

SRv6 configuration examples

Example: Configuring SRv6 that uses End SIDs

Network configuration

As shown in Figure 17, run OSPFv3 on Router A, Router B, and Router C. Set up an SRv6 tunnel between Router A and Router C.

Figure 17 Network diagram

‌

Table 1 Interface and IP address assignment

Device	Interface	IP address	Device	Interface	IP address
Router A	Loop0	1::9/128	Router C	Loop0	5::9/128
	GE0/0/2	1::1/64		GE0/0/2	2::2/64
Router B	Loop0	2::9/128
	GE0/0/1	1::2/64
	GE0/0/2	2::1/64

‌

Procedure

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

2. Configure OSPFv3 to advertise routes for the interfaces, including the loopback interfaces. (Details not shown.)

Execute the display ipv6 routing-table command on each router to verify that they have obtained routes to reach one another, including the host routes of loopback interfaces.

3. Configure Router A:

# Configure SRv6 End SIDs.

[RouterA] segment-routing ipv6

[RouterA-segment-routing-ipv6] locator aa ipv6-prefix 100:1::1 96 static 8

[RouterA-segment-routing-ipv6-locator-aa] opcode 1 end

[RouterA-segment-routing-ipv6-locator-aa] quit

[RouterA-segment-routing-ipv6] quit

# Configure OSPFv3 to advertise the SRv6 SIDs.

[RouterA] ospfv3 1

[RouterA-ospfv3-1] segment-routing ipv6 locator aa

[RouterA-ospfv3-1] quit

# Configure SID list a and specify Router B and Router C as nodes in the list.

[RouterA] ipv6 segment-routing sid-list a

[RouterA-srv6-sid-list-a] sid 200:1::1

[RouterA-srv6-sid-list-a] sid 300:1::1

[RouterA-srv6-sid-list-a] quit

# Create SRv6 tunnel interface Tunnel 1 on Router A. Specify Loopback 0 as the source interface, specify the IP address of Loopback 0 on Router C as the destination, configure an IPv6 address for the tunnel interface, and apply SID list a to the SRv6 tunnel.

[RouterA] interface tunnel 0 mode sr ipv6

[RouterA-Tunnel0] source loopback 0

[RouterA-Tunnel0] destination 5::9

[RouterA-Tunnel0] ipv6 address 6::6 64

[RouterA-Tunnel0] tunnel sid-list a

[RouterA-Tunnel0] quit

# Configure a static route to direct traffic destined for Router C to the SRv6 tunnel.

[RouterA] ipv6 route-static 99::1 64 tunnel 0

4. Configure Router B:

# Configure SRv6 End SIDs.

[RouterB] segment-routing ipv6

[RouterB-segment-routing-ipv6] locator bb ipv6-prefix 200:1::1 96 static 8

[RouterB-segment-routing-ipv6-locator-bb] opcode 1 end

[RouterB-segment-routing-ipv6-locator-bb] quit

[RouterB-segment-routing-ipv6] quit

# Configure OSPFv3 to advertise the SRv6 SIDs.

[RouterB] ospfv3 1

[RouterB-ospfv3-1] segment-routing ipv6 locator bb

[RouterB-ospfv3-1] quit

5. Configure Router C:

# Configure SRv6 End SIDs.

[RouterC] segment-routing ipv6

[RouterC-segment-routing-ipv6] locator cc ipv6-prefix 300:1::1 96 static 8

[RouterC-segment-routing-ipv6-locator-cc] opcode 1 end

[RouterC-segment-routing-ipv6-locator-cc] quit

[RouterC-segment-routing-ipv6] quit

# Configure OSPFv3 to advertise the SRv6 SIDs.

[RouterC] ospfv3 1

[RouterC-ospfv3-1] segment-routing ipv6 locator cc

[RouterC-ospfv3-1] quit

# Configure an SID list, SRv6 tunnel, and static route on Router C in the same way as the settings are configured on Router A. The SID list, SRv6 tunnel, and static route on Router C are from Router C to Router A. (Details not shown.)

Verifying the configuration

# Verify the SID list information on Router A.

[RouterA] display ipv6 segment-routing sid-list

SID list name: a

SID information:

SID index Address

5 200:1::1

9 300:1::1

SID list usage on tunnels:

Tunnel number SID list role

0 Primary

Verify that the traffic destined for 99::1 is forwarded through the SRv6 tunnel.

[Router A] display ipv6 fib 99::1

FIB entry count: 1

Flag:

U:Usable G:Gateway H:Host B:Blackhole D:Dynamic S:Static

R:Relay F:FRR

Destination: 99:: Prefix length: 64

Nexthop : :: Flags: US

Time stamp : 0x10 Label: Null

Interface : Tun0 Token: Invalid

Example: Configuring SRv6 that uses End.X SIDs

Network configuration

As shown in Figure 18, run OSPFv3 on Router A, Router B, and Router C. Set up an SRv6 tunnel between Router A and Router C.

Figure 18 Network diagram

‌

Table 2 Interface and IP address assignment

Device	Interface	IP address	Device	Interface	IP address
Router A	Loop0	1::9/128	Router C	Loop0	5::9/128
	GE0/0/2	1::1/64		GE0/0/2	2::2/64
Router B	Loop0	2::9/128
	GE0/0/1	1::2/64
	GE0/0/2	2::1/64

‌

Procedure

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

2. Configure OSPFv3 to advertise routes for the interfaces, including the loopback interfaces. (Details not shown.)

Execute the display ipv6 routing-table command on each router to verify that they have obtained routes to reach one another, including the host routes of loopback interfaces.

3. Configure Router A:

# Configure SRv6 End.X SIDs.

[RouterA] segment-routing ipv6

[RouterA-segment-routing-ipv6] locator a1 ipv6-prefix 100:1::1:0 96 static 8

[RouterA-segment-routing-ipv6-locator-a1] opcode 1 end-x interface gigabitethernet 0/0/2 nexthop 1::2

[RouterA-segment-routing-ipv6-locator-a1] quit

[RouterA-segment-routing-ipv6] quit

# Configure OSPFv3 to advertise the SRv6 SIDs.

[RouterA] ospfv3 1

[RouterA-ospfv3-1] segment-routing ipv6 locator a1

[RouterA-ospfv3-1] quit

# Configure SID list A and specify Router B and Router C as nodes in the list.

[RouterA] ipv6 segment-routing sid-list A

[RouterA-srv6-sid-list-A] sid 200:1::1:1

[RouterA-srv6-sid-list-A] sid 300:1::1:1

[RouterA-srv6-sid-list-A] quit

[RouterA] interface tunnel 0 mode sr ipv6

[RouterA-Tunnel0] source loopback 0

[RouterA-Tunnel0] destination 5::9

[RouterA-Tunnel0] ipv6 address 7::7 64

[RouterA-Tunnel0] tunnel sid-list A

[RouterA-Tunnel0] quit

# Configure a static route to direct traffic destined for Router C to the SRv6 tunnel.

[RouterA] ipv6 route-static 199::1 64 tunnel 0

4. Configure Router B:

# Configure SRv6 End.X SIDs.

[RouterB] segment-routing ipv6

[RouterB-segment-routing-ipv6] locator b1 ipv6-prefix 200:1::1:0 96 static 8

[RouterB-segment-routing-ipv6-locator-b1] opcode 1 end-x interface gigabitethernet 0/0/2 nexthop 2::2

[RouterB-segment-routing-ipv6-locator-b1] quit

[RouterB-segment-routing-ipv6] quit

# Configure OSPFv3 to advertise the SRv6 SIDs.

[RouterB] ospfv3 1

[RouterB-ospfv3-1] segment-routing ipv6 locator b1

[RouterB-ospfv3-1] quit

5. Configure Router C:

# Configure SRv6 End SIDs.

[RouterC] segment-routing ipv6

[RouterC-segment-routing-ipv6] locator c1 ipv6-prefix 300:1::1:0 96 static 8

[RouterC-segment-routing-ipv6-locator-c1] opcode 1 end

[RouterC-segment-routing-ipv6-locator-c1] quit

[RouterC-segment-routing-ipv6] quit

# Configure OSPFv3 to advertise the SRv6 SIDs.

[RouterC] ospfv3 1

[RouterC-ospfv3-1] segment-routing ipv6 locator c1

[RouterC-ospfv3-1] quit

Verifying the configuration

# Verify the SID list information on Router A.

[RouterA] display ipv6 segment-routing sid-list

SID list name: A

SID information:

SID index Address

5 200:1::1:1

9 300:1::1:1

SID list usage on tunnels:

Tunnel number SID list role

0 Primary

Verify that the traffic destined for 199::1 is forwarded through the SRv6 tunnel.

[Router A] display ipv6 fib 199::1

FIB entry count: 1

Flag:

U:Usable G:Gateway H:Host B:Blackhole D:Dynamic S:Static

R:Relay F:FRR

Destination: 199:: Prefix length: 64

Nexthop : :: Flags: US

Time stamp : 0x17 Label: Null

Interface : Tun0 Token: Invalid

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

‌

Table 3 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
	GE0/0/1	2000:1::1/64		GE0/0/1	2000:1::2/64
	GE0/0/2	2000:4::1/64		GE0/0/2	2000:2::2/64
Device C	Loop1	3::3/128	Device D	Loop1	4::4/128
	GE0/0/1	2000:3::3/64		GE0/0/1	2000:3::4/64
	GE0/0/2	2000:2::3/64		GE0/0/2	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 gigabitethernet 0/0/1

[DeviceA-GigabitEthernet0/0/1] isis ipv6 enable 1

[DeviceA-GigabitEthernet0/0/1] isis cost 10

[DeviceA-GigabitEthernet0/0/1] quit

[DeviceA] interface gigabitethernet 0/0/2

[DeviceA-GigabitEthernet0/0/2] isis ipv6 enable 1

[DeviceA-GigabitEthernet0/0/2] isis cost 10

[DeviceA-GigabitEthernet0/0/2] 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.

[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

[DeviceA-isis-1-ipv6] quit

[DeviceA-isis-1] quit

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

[DeviceA] isis 1

[DeviceA-isis-1] address-family ipv6

[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 gigabitethernet 0/0/1

[DeviceB-GigabitEthernet0/0/1] isis ipv6 enable 1

[DeviceB-GigabitEthernet0/0/1] isis cost 10

[DeviceB-GigabitEthernet0/0/1] quit

[DeviceB] interface gigabitethernet 0/0/2

[DeviceB-GigabitEthernet0/0/2] isis ipv6 enable 1

[DeviceB-GigabitEthernet0/0/2] isis cost 10

[DeviceB-GigabitEthernet0/0/2] 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

# Enable 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 gigabitethernet 0/0/1

[DeviceC-GigabitEthernet0/0/1] isis ipv6 enable 1

[DeviceC-GigabitEthernet0/0/1] isis cost 10

[DeviceC-GigabitEthernet0/0/1] quit

[DeviceC] interface gigabitethernet 0/0/2

[DeviceC-GigabitEthernet0/0/2] isis ipv6 enable 1

[DeviceC-GigabitEthernet0/0/2] isis cost 100

[DeviceC-GigabitEthernet0/0/2] 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

# Enable 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 gigabitethernet 0/0/1

[DeviceD-GigabitEthernet0/0/1] isis ipv6 enable 1

[DeviceD-GigabitEthernet0/0/1] isis cost 100

[DeviceD-GigabitEthernet0/0/1] quit

[DeviceD] interface gigabitethernet 0/0/2

[DeviceD-GigabitEthernet0/0/2] isis ipv6 enable 1

[DeviceD-GigabitEthernet0/0/2] isis cost 10

[DeviceD-GigabitEthernet0/0/2] 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

# Enable 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

Interface : GE0/0/1

TI-LFA:

Interface : GE0/0/2

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.

11-Segment Routing Configuration Guide

Basic concepts

SR node

SID

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

TI-LFA FRR protection types

Protocols and standards

Prerequisites for SRv6

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure

Specifying a source address for the outer IPv6 header of SRv6-encapsulated packets

Restrictions and guidelines

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

About this task

Prerequisites

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Procedure

About this task

Procedure

About this task

Procedure

About this task

Restrictions and guidelines for directing traffic to an SRv6 tunnel

Prerequisites for directing traffic to an SRv6 tunnel

Configuring the IPv6 router ID and enabling IPv6 TE

Configuring IGP shortcut

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

Procedure

About this task

Configuring IPv6 IS-IS SR microloop avoidance

Configuring OSPFv3 SR microloop avoidance

About this task

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure

Verifying and maintaining SRv6

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration