30.2.6 BGP4 + learned route filtering [SL-L3A]

<Structure of this section>

(1) Learning Conditional Routes Common to All Peers

Configure the switch to learn BGP4+ routes to any destination network except the routes in the 3ffe:501::/32 range.

Points to note

The example below shows how to use the distribute-list in command to apply learned route filtering consistently among all peers. To filter routes by destination network, use an ipv6 prefix-list filter.

First, configure an ipv6 prefix-list filter to deny routes in the 3ffe:501::/32 range. Then, by referencing this filter from the distribute-list in command, configure BGP4+ to filter learned routes by destination network.

Command examples

(config)# ipv6 prefix-list LONGER3ffe0501DENY seq 10 deny 3ffe:501::/32 ge 32 le 128

(config)# ipv6 prefix-list LONGER3ffe0501DENY seq 20 permit ::/0 ge 0 le 128

Configures prefix-list to deny prefixes in the 3ffe:501::/32 range but permits all other prefixes.
(config)# router bgp 65531

(config-router)# address-family ipv6

(config-router-af)# distribute-list prefix-list LONGER3ffe0501DENY in

Configures the switch to apply learned route filtering by the specified prefix-list filter to all peers.
(config-router-af)# end

# clear ipv6 bgp * in

Applies the changes to the learned route filtering configuration.

(2) Learning peer-specific conditional routes

The following shows how to configure BGP4+ to learn routes received from external peers that have an AS_PATH attribute of 65532 65533 and are not destined for the 3ffe:501::/32 address range. The switch assigns a value of 200 to the LOCAL_PREF attribute of learned routes. Other routes are not learned.

Points to note

The example below shows how to use the neighbor in command to apply learned route filtering to routes learned from individual BGP4+ peers. Use route-map to filter a route by conditions other than its destination network, or to modify some of its attributes.

First, configure a prefix-list filter to permit routes in the 3ffe:501::/32 range, and an ip as-path access-list filter to permit routes with an AS_PATH attribute of 65532 65533. Next, configure route-map to combine these two conditions. Finally, set the neighbor in command for peers that you want to filter by these conditions.

Command examples

(config)# ipv6 prefix-list LONGER3ffe0501 seq 10 permit 3ffe:501::/32 ge 32 le 128

Configures prefix-list to permit routes whose prefix is within the 3ffe:501::/32 range.
(config)# ip as-path access-list 2 permit "^65532_65533$"

Configures an ip as-path access-list filter to permit routes with an AS_PATH attribute of 65532 65533.
(config)# route-map BGP65532IN deny 10

(config-route-map)# match ipv6 address prefix-list LONGER3ffe0501

(config-route-map)# exit

Configures the route-map filter BGP65502IN to deny routes destined for the 3ffe:501::/32 address range.
(config)# route-map BGP65532IN permit 20

(config-route-map)# match as-path 2

(config-route-map)# set local-preference 200

(config-route-map)# exit

Configures route-map to assign a value of 200 to the LOCAL_PREF attribute of routes whose AS_PATH attribute matches 65532 65533, and permit those routes. Because BGP65532IN has no other conditions, the filter denies routes that do not match any of the conditions set so far.
(config)# router bgp 65531

(config-router)# neighbor 3ffe:502:811:1::1 remote-as 65532

(config-router)# address-family ipv6

(config-router-af)# neighbor 3ffe:502:811:1::1 route-map BGP65532IN in

Configures BGP4+ to use the route-map filter BGP65532IN to filter routes received from external peers.
(config-router-af)# end

# clear ipv6 bgp * in

Applies the changes to the learned route filtering configuration.