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AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 CLI-based Typical Configuration Examples

Example for Applying the AS-Path Attribute to a Route-Policy

Example for Applying the AS-Path Attribute to a Route-Policy

Applicability

This example applies to all models of AR routers in all versions.

Networking Requirements

As shown in Figure 8-28, four routers belong to different ASs and establish EBGP connections. When RouterD sends routes to RouterA, the AS-Path attribute needs to be changed so that route from RouterA to 192.168.6.1/24 is changed.

Figure 8-28 Networking diagram of applying the AS-Path attribute to a route-policy

Procedure

  1. Configure RouterA.

    #
 sysname RouterA
#
interface GigabitEthernet1/0/0
 ip address 192.168.1.1 255.255.255.0
#
interface GigabitEthernet2/0/0
 ip address 192.168.2.1 255.255.255.0
#
interface LoopBack0
 ip address 1.1.1.1 255.255.255.255
#
bgp 100
 router-id 1.1.1.1  //Set the router ID. You are advised to set the IP address of Loopback 0 as the router ID.
 peer 192.168.1.2 as-number 200  //Specify the peer IP address and AS number.
 peer 192.168.2.2 as-number 400
 #
 ipv4-family unicast
  undo synchronization
  peer 192.168.1.2 enable
  peer 192.168.2.2 enable
#

  2. Configure RouterB.

    #
 sysname RouterB
#
interface GigabitEthernet1/0/0
 ip address 192.168.3.1 255.255.255.0
#
interface GigabitEthernet2/0/0
 ip address 192.168.2.2 255.255.255.0
#
interface LoopBack0
 ip address 2.2.2.2 255.255.255.255
#
bgp 200
 router-id 2.2.2.2
 peer 192.168.2.1 as-number 100
 peer 192.168.3.2 as-number 300
 #
 ipv4-family unicast
  undo synchronization
  peer 192.168.2.1 enable
  peer 192.168.3.2 enable
#

  3. Configure RouterC.

    #
 sysname RouterC
#
interface GigabitEthernet1/0/0
 ip address 192.168.3.2 255.255.255.0
#
interface GigabitEthernet2/0/0
 ip address 192.168.4.2 255.255.255.0
#
interface LoopBack0
 ip address 3.3.3.3 255.255.255.255
#
bgp 300
 router-id 3.3.3.3
 peer 192.168.3.1 as-number 200
 peer 192.168.4.1 as-number 400
 #
 ipv4-family unicast
  undo synchronization
  peer 192.168.3.1 enable
  peer 192.168.4.1 enable
#

  4. Configure RouterD.

    #
 sysname RouterD
#
interface GigabitEthernet1/0/0
 ip address 192.168.1.2 255.255.255.0
#
interface GigabitEthernet2/0/0
 ip address 192.168.4.1 255.255.255.0
#
interface GigabitEthernet3/0/0
 ip address 192.168.6.1 255.255.255.0
#
interface LoopBack0
 ip address 4.4.4.4 255.255.255.255
#
bgp 400
 router-id 4.4.4.4
 peer 192.168.1.1 as-number 100
 peer 192.168.4.2 as-number 300
 #
 ipv4-family unicast
  undo synchronization
  network 192.168.6.0 255.255.255.0  //Configure BGP to advertise local routes.
  peer 192.168.1.1 enable
  peer 192.168.1.1 route-policy t1 export  //Apply a route-policy to the advertised routes.
  peer 192.168.4.2 enable
#
route-policy t1 permit node 5  //Create a route-policy.
 apply as-path 400 400 400 additive  //Add AS number 400 400 400 to the AS-Path list.
#

  5. Verify the configuration.

    # Before a route-policy is applied to RouterD, run the display bgp routing-table command on RouterA. You can see that there are two BGP routes destined for 192.168.6.0/24. A route with next-hop address 192.168.2.2 has AS-Path 200 300 400, and the other route with next-hop address 192.168.1.2 has AS-Path 400. Then run the display ip routing-table command. You can see that the route with next-hop address 192.168.1.2 is preferred.

    # After a route-policy is applied to RouterD, run the display bgp routing-table command on RouterA. You can see that there are two BGP routes destined for 192.168.6.0/24. A route with next-hop address 192.168.2.2 has AS-Path 200 300 400, and the other route with next-hop address 192.168.1.2 has AS-Path 400,400,400,400. Then run the display ip routing-table command. You can see that the route with next-hop address 192.168.2.2 is preferred.

Configuration Notes

  • If no mask or mask length is specified in the network command, the IP address in the network command is considered as a classful address.
  • By default, IGP-BGP synchronization is disabled.
  • By default, peers are automatically enabled in the BGP-IPv4 unicast address family view.