BGP: Attribute-map configuration and verification

BGP: Attribute-map configuration and verification

·         Whenever BGP summarizes along with AS-SET key-word, the summarized route inherits the properties of individual routes.

·         Example: If any of the individual route has community value, the summarized route inherits this community value

·         If it is a special community value like no-export, it affects the propagation of the summarized route.

·         We can use ATTRIBUTE-MAP to change the properties (attributes) of the summarized route).

·         Let me take a small topology to configure this:

R1----------------------R2--------------------R3

·         R1: AS 100

·         R2: AS 200

·         R3: AS 300

·         Configure 5 loopbacks 10.1.1.1, 10.1.2.1, 10.1.3.1, 10.1.4.1, 10.1.5.1 in R1 and advertise them into BGP

·         Configure 10.1.1.1 with no-export community

·         Configure aggregate-address in R2 and see the properties of summarized route.

·         Then we will see how to configure ATTRIBUTE-MAP to change this inherited properties

R1(config-router)#do show run | begin router bgp

router bgp 100

 no synchronization

 bgp router-id 1.1.1.1

 bgp log-neighbor-changes

 network 10.1.1.1 mask 255.255.255.255

 network 10.1.2.1 mask 255.255.255.255

 network 10.1.3.1 mask 255.255.255.255

 network 10.1.4.1 mask 255.255.255.255

 network 10.1.5.1 mask 255.255.255.255

 neighbor 100.1.12.2 remote-as 200

 neighbor 100.1.12.2 send-community

 neighbor 100.1.12.2 route-map EXPORT out

 no auto-summary

!

!

ip prefix-list 10 seq 5 permit 10.1.1.1/32

!

route-map EXPORT permit 10

 match ip address prefix-list 10

 set community no-export

!

route-map EXPORT permit 100

!

R1(config-router)#!

R2(config-router)#do show run | begin router bgp 200

router bgp 200

 no synchronization

 bgp log-neighbor-changes

 aggregate-address 10.1.0.0 255.255.0.0

 neighbor 100.1.12.1 remote-as 100

 neighbor 100.1.23.3 remote-as 300

 neighbor 100.1.23.3 send-community

 no auto-summary

!

R2#show ip bgp

BGP table version is 23, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.0.0/16      0.0.0.0                            32768 i

*> 10.1.1.1/32      100.1.12.1               0             0 100 i

*> 10.1.2.1/32      100.1.12.1               0             0 100 i

*> 10.1.3.1/32      100.1.12.1               0             0 100 i

*> 10.1.4.1/32      100.1.12.1               0             0 100 i

*> 10.1.5.1/32      100.1.12.1               0             0 100 i

R2#

R2#show ip bgp 10.1.1.1

BGP routing table entry for 10.1.1.1/32, version 22

Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)

  Not advertised to any peer

  100

    100.1.12.1 from 100.1.12.1 (1.1.1.1)

      Origin IGP, metric 0, localpref 100, valid, external, best

      Community: no-export

R2#

R2#show ip bgp 10.1.0.0/16

BGP routing table entry for 10.1.0.0/16, version 23

Paths: (1 available, best #1, table Default-IP-Routing-Table)

  Advertised to update-groups:

     1          2

  Local, (aggregated by 200 2.2.2.2)

    0.0.0.0 from 0.0.0.0 (2.2.2.2)

      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, atomic-aggregate, best

R2#

Observations:

·         I have not configured AS-SET key-word while configuring the aggregate-address

·         So, I don’t see the summarized route inheriting the community no-export that is configured for 10.1.1.1

·         Let me configure AS-SET key-word while configuring the aggregate-address:

R2(config-router)#aggregate-address 10.1.0.0 255.255.0.0 as-set

R2(config-router)#do clear ip bgp *

R2(config-router)#

*Jun 28 09:58:09.627: %BGP-5-ADJCHANGE: neighbor 100.1.12.1 Down User reset

*Jun 28 09:58:09.631: %BGP-5-ADJCHANGE: neighbor 100.1.23.3 Down User reset

R2(config-router)#

*Jun 28 09:58:10.827: %BGP-5-ADJCHANGE: neighbor 100.1.12.1 Up

*Jun 28 09:58:10.915: %BGP-5-ADJCHANGE: neighbor 100.1.23.3 Up

R2(config-router)#end

R2#show i

*Jun 28 10:37:40.207: %SYS-5-CONFIG_I: Configured from console by console

R2#show ip bgp 10.1.0.0/16

BGP routing table entry for 10.1.0.0/16, version 7

Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)

  Not advertised to any peer

  100, (aggregated by 200 2.2.2.2)

    0.0.0.0 from 0.0.0.0 (2.2.2.2)

      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best

      Community: no-export

R2#

R3#show ip bgp

BGP table version is 41, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.2.1/32      100.1.23.2                             0 200 100 i

*> 10.1.3.1/32      100.1.23.2                             0 200 100 i

*> 10.1.4.1/32      100.1.23.2                             0 200 100 i

*> 10.1.5.1/32      100.1.23.2                             0 200 100 i

R3#

Observations:

·         If I configure the aggregate-address with AS-SET key-word, then the summarized route inherited the properties of 10.1.1.1, no-export community.

·         That is the reason why R2 didn’t advertise this summarized route to R3.

·         Configuring the ATTRIBUTE-MAP while configuring the aggregate-address to change the community value:

R2(config)#route-map ATTRIB

R2(config-route-map)#set community none

R2(config-route-map)#router bgp 200

R2(config-router)#aggregate-address 10.1.0.0 255.255.0.0 as-set attribute-map ATTRIB

R2(config-router)#DO CLEAR IP BGP *

R2(config-router)#

*Jun 28 14:06:31.566: %BGP-5-ADJCHANGE: neighbor 100.1.12.1 Down User reset

*Jun 28 14:06:31.570: %BGP-5-ADJCHANGE: neighbor 100.1.23.3 Down User reset

R2(config-router)#

*Jun 28 14:06:32.774: %BGP-5-ADJCHANGE: neighbor 100.1.23.3 Up

*Jun 28 14:06:33.118: %BGP-5-ADJCHANGE: neighbor 100.1.12.1 Up

R2(config-router)#

R2#show ip bgp 10.1.0.0/16

BGP routing table entry for 10.1.0.0/16, version 7

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Flag: 0x820

  Advertised to update-groups:

     1          2

  100, (aggregated by 200 2.2.2.2)

    0.0.0.0 from 0.0.0.0 (2.2.2.2)

      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best

R2#

R3#show ip bgp

BGP table version is 52, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.0.0/16      100.1.23.2               0             0 200 100 i

*> 10.1.2.1/32      100.1.23.2                             0 200 100 i

*> 10.1.3.1/32      100.1.23.2                             0 200 100 i

*> 10.1.4.1/32      100.1.23.2                             0 200 100 i

*> 10.1.5.1/32      100.1.23.2                             0 200 100 i

R3#

Observation:

·         I have set the community value to none using the ATTRIBUTE-MAP

·         That’s why R2 has advertised this route to R3 now.