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Configuration Guide - IP Unicast Routing

CloudEngine 12800 and 12800E V200R002C50

This document describes the configurations of IP Unicast Routing, including IP Routing, Static Route, RIP, RIPng, OSPF, OSPFv3, IPv4 IS-IS, IPv6 IS-IS, BGP, Routing Policy, and PBR.

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Configuring the Next_Hop Attribute

Configuring the Next_Hop Attribute

Context

When an Autonomous System Boundary Router (ASBR) forwards the route learned from an EBGP peer to an IBGP peer, the ASBR does not change the next hop of the route by default. When the IBGP peer receives this route, it finds the next hop unreachable, sets the route to inactive, and does not use this route to guide traffic forwarding. To enable the IBGP peer to use this route to guide traffic forwarding, configure the ASBR to set its IP address as the next hop of the route when the ASBR forwards this route to the IBGP peer. After the IBGP peer receives the route from the ASBR, it finds the next hop of the route reachable, sets the route to active, and uses this route to guide traffic forwarding.

When a BGP route changes, BGP needs to iterate the indirect next hop of the route again. If no restriction is imposed on the iterated route, BGP may iterate the next hop to an incorrect forwarding path, causing traffic loss. To prevent traffic loss, configure routing policy-based route iteration.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run bgp { as-number-plain | as-number-dot }

    The BGP view is displayed.

  3. Enter the corresponding address family view based on network type to configure BGP devices on networks.

    • Run ipv4-family unicast

      The BGP-IPv4 unicast address family view is displayed.

    • Run ipv4-family multicast

      The BGP-IPv4 multicast address family view is displayed.

    • Run ipv4-family vpnv4 [ unicast ]

      The BGP-VPNv4 address family view is displayed.

    • Run ipv4-family vpn-instance vpn-instance-name

      The BGP-VPN instance IPv4 address family view is displayed.

    • Run ipv6-family [ unicast ]

      The BGP-IPv6 unicast address family view is displayed.

    • Run ipv6-family vpnv6 [ unicast ]

      The BGP-VPNv6 address family view is displayed.

    • Run ipv6-family vpn-instance vpn-instance-name

      The BGP-VPN instance IPv6 address family view is displayed.

  4. Perform any of the following operations as required:
    • Run peer { ipv4-address | group-name | ipv6-address } next-hop-local

      A BGP device is configured to set its IP address as the next hop when the device advertises routes to an IBGP peer or an IBGP peer group.

      By default, a BGP device does not change the next-hop address when advertising routes to its IBGP peers.

    • Run nexthop recursive-lookup route-policy route-policy-name

      Routing-policy-based next hop iteration is configured.

      By default, routing-policy-based next hop iteration is not configured.

    • Run the following command in the IPv4 unicast address family view: peer { ipv4-address | group-name } next-hop-invariable

      The device is prevented from changing the next-hop address of a route imported from an IGP before advertising the route to an IBGP peer.

      By default, a device changes the next-hop address of a route imported from an IGP to the address of the interface connecting the device to its peer when advertising the route to an IBGP peer.

    • Run the following command in the IPv4 unicast address family view: nexthop third-party

      The device is prevented from changing the next-hop address of a route when the device advertises the route to a peer in the specified scenarios.

      The default configurations are as follows:
      • Before advertising a route that is learned from a directly connected peer to a directly connected EBGP peer, the device changes the next hop of the route to the IP address of the local interface that is used to establish the BGP peer relationship with the EBGP peer.
      • Before advertising a locally imported route to a directly connected IBGP or EBGP peer, the device changes the next hop of the route to the IP address of the local interface that is used to establish the BGP peer relationship with the IBGP or EBGP peer.

    NOTE:

    The nexthop recursive-lookup route-policy route-policy-name command does not take effect for the routes received from directly connected EBGP peers.

  5. Run commit

    The configuration is committed.

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Updated: 2019-03-21

Document ID: EDOC1000166601

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