IP routing directs IP packet forwarding on routers. Based on the destination IP address in the packet, a router looks up a route for the packet in a routing table and forwards the packet to the next hop. Routes are path information used to direct IP packets.

Routing table

A RIB contains the global routing information and related information, including route recursion, route redistribution, and route extension information. The router selects optimal routes from the routing table and puts them into the FIB table. It uses the FIB table to forward packets. For more information about the FIB table, see Layer 3—IP Services Configuration Guide.

Route categories

Table 1 categorizes routes by different criteria.

Table 1 Route categories

Criterion	Categories
Origin	· Direct route—A direct route is discovered by the data link protocol on an interface, and is also called an interface route. · Static route—A static route is manually configured by an administrator. · Dynamic route—A dynamic route is dynamically discovered by a routing protocol.
Destination	· Network route—The destination is a network. The subnet mask is less than 32 bits. · Host route—The destination is a host. The subnet mask is 32 bits.
Whether the destination is directly connected	· Direct route—The destination is directly connected. · Indirect route—The destination is indirectly connected.

Dynamic routing protocols

Static routes work well in small, stable networks. They are easy to configure and require fewer system resources. However, in networks where topology changes occur frequently, a typical practice is to configure a dynamic routing protocol. Compared with static routing, a dynamic routing protocol is complicated to configure, requires more router resources, and consumes more network resources.

Dynamic routing protocols dynamically collect and report reachability information to adapt to topology changes. They are suitable for large networks.

Dynamic routing protocols can be classified by different criteria, as shown in Table 2.

Table 2 Categories of dynamic routing protocols

Criterion	Categories
Operation scope	· IGPs—Work within an AS. Examples include RIP, OSPF, and IS-IS. · EGPs—Work between ASs. The most popular EGP is BGP.
Routing algorithm	· Distance-vector protocols—Examples include RIP and BGP. BGP is also considered a path-vector protocol. · Link-state protocols—Examples include OSPF and IS-IS.
Destination address type	· Unicast routing protocols—Examples include RIP, OSPF, BGP, and IS-IS. · Multicast routing protocols—Examples include PIM-SM and PIM-DM.
IP version	· IPv4 routing protocols—Examples include RIP, OSPF, BGP, and IS-IS. · IPv6 routing protocols—Examples include RIPng, OSPFv3, IPv6 BGP, and IPv6 IS-IS.

An AS refers to a group of routers that use the same routing policy and work under the same administration.

Route preference

Routing protocols, including static and direct routing, each by default have a preference. If they find multiple routes to the same destination, the router selects the route with the highest preference as the optimal route.

The preference of a direct route is always 0 and cannot be changed. You can configure a preference for each static route and each dynamic routing protocol. The following table lists the route types and default preferences. The smaller the value, the higher the preference.

Table 3 Route types and default route preferences

Route type	Preference
Direct route	0
Multicast static route	1
OSPF	10
IS-IS	15
Unicast static route	60
RIP	100
OSPF ASE	150
OSPF NSSA	150
IBGP	255
EBGP	255
Unknown (route from an untrusted source)	256

Load sharing

A routing protocol might find multiple optimal equal-cost routes to the same destination. You can use these routes to implement equal-cost multi-path (ECMP) load sharing.

Static routing, IPv6 static routing, RIP, RIPng, OSPF, OSPFv3, BGP, IPv6 BGP, IS-IS, and IPv6 IS-IS support ECMP load sharing.

Route backup

Route backup can improve network availability. Among multiple routes to the same destination, the route with the highest priority is the primary route and others are secondary routes.

The router forwards matching packets through the primary route. When the primary route fails, the route with the highest preference among the secondary routes is selected to forward packets. When the primary route recovers, the router uses it to forward packets.

Route recursion

To use a static, BGP, or RIP route that has an indirectly connected next hop, a router must perform route recursion to find the output interface to reach the next hop.

Link-state routing protocols, such as OSPF and IS-IS, do not need route recursion, because they obtain directly connected next hops through route calculation.

The RIB records and saves route recursion information, including brief information about related routes, recursive paths, and recursion depth.

Route redistribution

Route redistribution enables routing protocols to learn routing information from each other. A dynamic routing protocol can redistribute routes from other routing protocols, including direct and static routing. For more information, see the respective chapters on those routing protocols in this configuration guide.

The RIB records redistribution relationships of routing protocols.

Extension attribute redistribution

Extension attribute redistribution enables routing protocols to learn route extension attributes from each other, including BGP extended community attributes, OSPF area IDs, route types, and router IDs.

The RIB records extended attributes of each routing protocol and redistribution relationships of different routing protocol extended attributes.

Restrictions and guidelines: Basic IP routing configuration

The device does not support basic IP routing features when it operates in advanced system operating mode. For more information about system operating modes, see device management in Fundamentals Configuration Guide.

Setting the maximum lifetime for routes and labels in the RIB

About this task

Perform this task to prevent routes of a certain protocol from being aged out due to slow protocol convergence resulting from a large number of route entries or long GR period.

Restrictions and guidelines

The configuration takes effect at the next protocol or RIB process switchover.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv4 address family and enter its view.

address-family ipv4

4. Set the maximum lifetime for IPv4 routes and labels in the RIB.

protocol protocol [ instance instance-name ] lifetime seconds

By default, the maximum lifetime for routes and labels in the RIB is 900 seconds.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv6 address family and enter its view.

address-family ipv6

4. Set the maximum lifetime for IPv6 routes and labels in the RIB.

protocol protocol [ instance instance-name ] lifetime seconds

By default, the maximum lifetime for routes and labels in the RIB is 900 seconds.

Setting the maximum lifetime for routes in the FIB

About this task

When GR is disabled, FIB entries must be retained for some time after a protocol process switchover or RIB process switchover. When GR is enabled, FIB entries must be removed immediately after a protocol or RIB process switchover to avoid routing issues. Perform this task to meet such requirements.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv4 address family and enter its view.

address-family ipv4

4. Set the maximum lifetime for IPv4 routes in the FIB.

fib lifetime seconds

By default, the maximum lifetime for routes in the FIB is 600 seconds.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv6 address family and enter its view.

address-family ipv6

4. Set the maximum lifetime for IPv6 routes in the FIB.

fib lifetime seconds

By default, the maximum lifetime for routes in the FIB is 600 seconds.

Enabling the RIB to flush route attribute information to the FIB

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv4 address family and enter its view.

address-family ipv4

4. Enable the RIB to flush route attribute information to the FIB.

flush route-attribute protocol

By default, the RIB does not flush route attribute information to the FIB.

Setting the maximum number of ECMP routes

Restrictions and guidelines

This configuration takes effect at reboot. Make sure the reboot does not impact your network.

Procedure (IPv4)

1. Enter system view.

system-view

2. Set the maximum number of ECMP routes.

max-ecmp-num number

By default, the maximum number of ECMP routes is 8.

Configuring the ECMP mode

About this task

An ECMP route group contains ECMP routes to the same destination. The following ECMP modes are supported:

· Normal mode—When one or multiple ECMP routes in an ECMP group fail, this mode enables the device to reallocate all traffic to the remaining routes in the ECMP group.

· Enhanced mode—When one or multiple ECMP routes in an ECMP group fail, this mode enables the device to reallocate only the traffic of the failed routes to the remaining routes.

· Compressed mode—This mode enables the device to compress the hardware resources of all ECMP route groups to save storage space for more ECMP route groups.

Restrictions and guidelines

This configuration takes effect at reboot. Make sure the reboot does not impact your network.

The task applies to both IPv4 and IPv6 ECMP routes.

Procedure

1. Enter system view.

system-view

2. Configure the ECMP mode.

ecmp mode { compressed | enhanced }

By default, the normal ECMP mode is used.

Configuring inter-protocol FRR

About this task

This feature is applicable to services that are sensitive to packet loss and latency. Inter-protocol fast reroute (FRR) enables fast rerouting between routes of different protocols. A backup next hop is automatically selected to reduce the service interruption time caused by unreachable next hops. When the next hop of the primary link fails, the traffic is redirected to the backup next hop.

Among the routes to the same destination in the RIB, a router adds the route with the highest preference to the FIB table. After you configure this feature, the device will select a route of another routing protocol as the backup route. When the next hop of the primary route is unreachable, the device forwards packets through the backup route.

Restrictions and guidelines

This feature uses the next hop of a route from a different protocol as the backup next hop, which might cause loops.

If you configure both inter-protocol FRR and FRR for the specified routing protocol, FRR for the specified routing protocol takes effect.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv4 address family and enter its view.

address-family ipv4

4. Enable IPv4 RIB inter-protocol FRR.

inter-protocol fast-reroute

By default, inter-protocol FRR is disabled.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv6 address family and enter its view.

address-family ipv6

4. Enable IPv6 RIB inter-protocol FRR.

inter-protocol fast-reroute

By default, inter-protocol FRR is disabled.

Configuring BFD for primary route next hop availability detection

About configuring BFD for primary route next hop detection

This feature uses BFD to detect the availability of the primary route next hop for inter-protocol FRR or ECMP routes. When the primary route next hop unreachable, this feature enables the upper layer routing protocol to reallocate service traffic to the backup next hops or to the remaining ECMP next hops.

For inter-protocol FRR, the primary route is the route with the highest preference among the routes to the same destination. If BFD detects that the next hop of the primary route is unreachable, it notifies the FIB of the issue. The FIB will use the backup next hops to guide traffic forwarding.

For ECMP routes of a routing protocol, the primary route is each ECMP route. If BFD detects that the next hop of an ECMP route is unreachable, it notifies the routing protocol of the issue. The routing protocol will reallocate the service traffic to the remaining ECMP next hops. When BFD detects that the next hops of all ECMP routes are invalid, BFD notifies the routing protocol to withdraw the routes. In addition, the device reselects optimal routes for the service traffic.

For more information about BFD, see High Availability Configuration Guide.

Restrictions and guidelines for configuring BFD for primary route next hop availability detection

If you specify the ecmp-shared keyword when configuring FRR for a routing protocol, the device will use the LFA algorithm to calculate backup next hops for each ECMP route. The routes destined for the backup next hops are also added to the routing table as ECMP routes and the state of these routes is backup. BFD does not detect these backup ECMP routes.

Configuring BFD control packet mode

About this task

This mode uses BFD control packets to detect the status of a link bidirectionally at a millisecond level.

Restrictions and guidelines for BFD control packet mode

A control-packet-mode BFD session can be successfully established through negotiation between the two ends. To use a control-packet-mode BFD session to detect the primary route next hop availability, you must create a static BFD session that meets the following requirements on the next hop device:

· Create a single-hop BFD session in control packet mode.

· The source IP address of the BFD session is the destination IP address of the BFD session automatically created by the local end.

· The destination IP address of the BFD session is the source IP address of the BFD session automatically created by the local end.

· The remote discriminator of the BFD session is the local discriminator of the BFD session automatically created by the local end.

The local device can use a control-packet-mode BFD session to detect the primary route next hop only after you create the static BFD session on the primary route next hop device.

Procedure

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create RIB IPv4 or IPv6 address family view and enter the view.

IPv4:

address-family ipv4

IPv6:

address-family ipv6

4. Enable BFD for primary link availability detection.

primary-path-detect bfd ctrl [ inter-protocol-frr | protocol-ecmp protocol ]

By default, BFD is disabled for primary link availability detection.

Configuring BFD echo packet mode

About this task

With BFD echo packet mode enabled, the output interface sends BFD echo packets to the destination device, and the device sends the packets back to test the link reachability.

Restrictions and guidelines

You do not need to configure BFD echo packet mode at the peer end.

Procedure

1. Enter system view.

system-view

2. (Optional.) Configure the source IP address of echo packets.

IPv4:

bfd echo-source-ip ip-address

By default, the source IPv4 address of echo packets is not configured.

As a best practice to avoid network congestion caused by excessive ICMP redirect packets from the peer, use this command. Make sure the source IPv4 address is not on the subnet of any interfaces on the device.

For more information about this command, see BFD in High Availability Command Reference.

IPv6:

bfd echo-source-ipv6 ipv6-address

By default, the source IPv6 address of echo packets is not configured.

As a best practice to avoid network congestion caused by excessive ICMPv6 redirect packets from the peer, use this command. Make sure the source IPv6 address is not on the subnet of any interfaces on the device.

You must specify a global unicast address as the source IPv6 address of BFD echo packets.

For more information about this command, see BFD in High Availability Command Reference.

3. Enter RIB view.

rib

4. Create RIB IPv4 or IPv6 address family view and enter the view.

IPv4:

address-family ipv4

IPv6:

address-family ipv6

5. Enable BFD for primary link availability detection.

primary-path-detect bfd echo [ inter-protocol-frr | protocol-ecmp protocol ]

By default, BFD is disabled for primary link availability detection.

Enabling route fast switchover

About this task

This feature applies to a device that provides the same physical output interface for large numbers of routes, including ECMP routes and primary/secondary routes. When a link failure occurs on the interface, the device must perform the following tasks before switching the traffic to another route:

1. Deletes all ARP or ND entries for the link.

2. Instructs the FIB to delete the associated FIB entries.

This procedure is time consuming and interrupts traffic for a long time. To resolve this problem, you can enable route fast switchover. This feature allows the device to instruct the FIB to delete the invalid FIB entries for route switchover first.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enable IPv4 route fast switchover.

ip route fast-switchover enable

By default, IPv4 route fast switchover is disabled.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enable IPv6 route fast switchover.

ipv6 route fast-switchover enable

By default, IPv6 route fast switchover is disabled.

Configuring the routing-mode hardware resource mode

About this task

This configuration requires a reboot to take effect. Before rebooting the device, make sure you fully understand the impact on your network.

The device supports the following routing-mode hardware resource modes:

· IPv6-64—Supports only IPv6 routes with prefixes equal to or shorter than 64 bits.

· IPv6-128—Supports IPv6 routes with prefixes longer than 64 bits.

Restrictions and guidelines

If you disable support for IPv6 routes with prefixes longer than 64 bits, IPv6 host routes with 128-bit prefix length do not support ECMP.

Procedure

1. Enter system view.

system-view

2. Configure the routing-mode hardware resource mode.

hardware-resource routing-mode { ipv6-64 | ipv6-128 }

By default, the routing-mode hardware resource mode is IPv6-128.

Configuring routing policy-based recursive lookup

About this task

Configure routing policy-based recursive lookup to control route recursion results. For example, when a route changes, the routing protocol has to perform a route recursion if the next hop is indirectly connected. The routing protocol might select an incorrect path, which can cause traffic loss. To prevent this problem, you can use a routing policy to filter out incorrect routes. The routes that pass the filtering of the routing policy will be used for route recursion.

Restrictions and guidelines

The apply clauses in the specified routing policy cannot take effect.

Make sure a minimum of one related route can match the routing policy for correct traffic forwarding.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv4 address family and enter its view.

address-family ipv4

4. Configure routing policy-based recursive lookup.

protocol protocol nexthop recursive-lookup route-policy route-policy-name

By default, routing policy-based recursive lookup is not configured.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv6 address family and enter its view.

address-family ipv6

4. Configure routing policy-based recursive lookup.

protocol protocol nexthop recursive-lookup route-policy route-policy-name

By default, routing policy-based recursive lookup is not configured.

Setting the maximum number of active routes supported by the device

About this task

To perform this task:

· You can use the routing-table limit number warn-threshold command to specify an alarm threshold. When the percentage of active routes exceeds the alarm threshold, the system generates a system log message but still accepts active routes. You can take relevant actions based on the message to save system resources. If the number of active routes reaches the maximum number, no more routes can be added and new routes are discarded.

· You can use the routing-table limit number simply-alert command to specify an alarm threshold. When the maximum number of active IPv4/IPv6 routes is exceeded, the device still accepts new active routes but generates a system log message. You can take relevant actions based on the message to save system resources.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv4 address family and enter its view.

address-family ipv4

4. Set the maximum number of active IPv4 routes supported by the device.

routing-table limit number { warn-threshold | simply-alert }

By default, the maximum number of active IPv4 routes is not set for the device.

Configuration in RIB IPv4 address family view limits the number of active IPv4 routes for the public network.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enter RIB view.

rib

3. Create the RIB IPv6 address family and enter its view.

address-family ipv6

4. Set the maximum number of active IPv6 routes supported by the device.

routing-table limit number { warn-threshold | simply-alert }

By default, the maximum number of active IPv6 routes is not set for the device.

Configuration in RIB IPv6 address family view limits the number of active IPv6 routes for the public network.

Enabling MTP

About this task

Use maintenance probe (MTP) to locate faults for routing protocols depending on your network maintenance requirements. MTP enables the device to automatically ping and tracert a neighbor upon expiration of the neighbor hold timer and record the ping and tracert results. To view detailed fault information, use the display commands of routing protocols, for example, the display bgp troubleshooting command. To view detailed MTP information, use the display logbuffer command.

Procedure

1. Enter system view.

system-view

2. Enable MTP.

maintenance-probe enable

By default, MTP is disabled.

Configuring RIB SNMP notifications

About this task

To report critical RIB events to an NMS, enable SNMP notifications for RIB. For SNMP notifications to be sent correctly, you must also configure SNMP on the device. For more information about SNMP configuration, see the network management and monitoring configuration guide for the device.

Procedure (IPv4)

1. Enter system view.

system-view

2. Enable IPv4 RIB SNMP notifications.

By default, IPv4 RIB SNMP notifications are enabled.

Procedure (IPv6)

1. Enter system view.

system-view

2. Enable IPv6 RIB SNMP notifications.

By default, IPv6 RIB SNMP notifications are enabled.

Display and maintenance commands for basic IP routing

Execute display commands in any view and reset commands in user view.

Task	Command
Display the ECMP mode.	display ecmp mode
Display the routing-mode hardware resource mode.	display hardware-resource routing-mode
Display routing table information.	display ip routing-table [ verbose ] display ip routing-table all-routes
Display information about routes permitted by an IPv4 basic ACL.	display ip routing-table acl ipv4-acl-number [ verbose ]
Display information about routes to a specific destination address.	display ip routing-table ip-address [ mask-length \| mask ] [ longer-match ] [ verbose ]
Display information about routes to a range of destination addresses.	display ip routing-table ip-address1 to ip-address2 [ verbose ]
Display information about routes permitted by an IP prefix list.	display ip routing-table prefix-list prefix-list-name [ verbose ]
Display information about routes installed by a protocol.	display ip routing-table protocol protocol [ inactive \| verbose ]
Display IPv4 route statistics.	display ip routing-table [ all-routes ] statistics
Display brief IPv4 routing table information.	display ip routing-table summary
Display route attribute information in the IPv6 RIB.	display ipv6 rib attribute [ attribute-id ]
Display IPv6 RIB GR state information.	display ipv6 rib graceful-restart
Display next hop information in the IPv6 RIB.	display ipv6 rib nib [ self-originated ] [ nib-id ] [ verbose ] display ipv6 rib nib protocol protocol [ verbose ]
Display next hop information for IPv6 direct routes.	display ipv6 route-direct nib [ nib-id ] [ verbose ]
Display IPv6 routing table information.	display ipv6 routing-table [ verbose ] display ipv6 routing-table all-routes
Display information about routes permitted by an IPv6 basic ACL.	display ipv6 routing-table acl ipv6-acl-number [ verbose ]
Display information about routes to an IPv6 destination address.	display ipv6 routing-table ipv6-address [ prefix-length ] [ longer-match ] [ verbose ]
Display information about routes to a range of IPv6 destination addresses.	display ipv6 routing-table ipv6-address1 to ipv6-address2 [ verbose ]
Display information about routes permitted by an IPv6 prefix list.	display ipv6 routing-table prefix-list prefix-list-name [ verbose ]
Display information about routes installed by an IPv6 protocol.	display ipv6 routing-table protocol protocol [ inactive \| verbose ]
Display IPv6 route statistics.	display ipv6 routing-table [ all-routes ] statistics
Display brief IPv6 routing table information.	display ipv6 routing-table summary
Display the maximum number of IPv4 ECMP routes.	display max-ecmp-num
Display route attribute information in the RIB.	display rib attribute [ attribute-id ]
Display RIB GR state information.	display rib graceful-restart
Display next hop information in the RIB.	display rib nib [ self-originated ] [ nib-id ] [ verbose ] display rib nib protocol protocol [ verbose ]
Display next hop information for direct routes.	display route-direct nib [ nib-id ] [ verbose ]
Clear IPv4 route statistics.	reset ip routing-table statistics protocol { protocol \| all } reset ip routing-table [ all-routes ] statistics protocol { protocol \| all }
Clear IPv6 route statistics.	reset ipv6 routing-table statistics protocol { protocol \| all } reset ipv6 routing-table [ all-routes ] statistics protocol { protocol \| all }

04-Layer 3—IP Routing Configuration Guide

Dynamic routing protocols

Route preference

Load sharing

Extension attribute redistribution

About this task

Restrictions and guidelines

Procedure (IPv4)

Procedure (IPv6)

About this task

Procedure (IPv4)

Procedure (IPv6)

Restrictions and guidelines

Procedure (IPv4)

About this task

Restrictions and guidelines

About this task

Restrictions and guidelines

Procedure (IPv4)

Procedure (IPv6)

About this task

Restrictions and guidelines for BFD control packet mode

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Procedure (IPv4)

Procedure (IPv6)

About this task

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure (IPv4)

Procedure (IPv6)

About this task

Procedure (IPv4)

Procedure (IPv6)

About this task

Procedure

About this task

Procedure (IPv4)

Procedure (IPv6)

Display and maintenance commands for basic IP routing

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