BGP attributes with summary address...RNS..vol 1 ..BGP ...7.35

As per the explannation .....With AS set parameter to the aggregate - address command , the resulting prefix will inherit  addiative attributes of the specific prefixes.This includes AS_PATH and community attribute which are grouped together from all prefixes.

in 7.35 RNS Vol 1 task......>R4 is tagging 112.0.0.0/8 with the community of "no-export".When R1 aggregate all the prefixes into one (i.e.112.0.0.0/5) the summary prefix should inherit the "No-export" community.

Rack1R4#sh ip bgp 112.0.0.0/8
BGP routing table entry for 112.0.0.0/8, version 11
Paths: (2 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)
  Advertised to update-groups:
        1
  54 50 60
    204.12.1.254 from 204.12.1.254 (31.3.0.1)
      Origin IGP, localpref 100, valid, external, best
      Community: no-export <-----------------------------------------community set
      DMZ-Link Bw 12500 kbytes
  54 50 60, (received-only)
    204.12.1.254 from 204.12.1.254 (31.3.0.1)
      Origin IGP, localpref 100, valid, external
      DMZ-Link Bw 12500 kbytes

Rack1R1#sh ip bgp 112.0.0.0/8
BGP routing table entry for 112.0.0.0/8, version 27
Paths: (2 available, best #1, table Default-IP-Routing-Table, Advertisements suppressed by an aggregate.)
  Not advertised to any peer
  54 50 60, (Received from a RR-client), (received & used)
    54.1.1.254 from 155.1.146.6 (150.1.6.6)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      DMZ-Link Bw 193 kbytes
  54 50 60, (Received from a RR-client)
    204.12.1.254 from 155.1.146.4 (223.255.255.255)
      Origin IGP, metric 0, localpref 100, valid, internal
      Community: no-export <----------------------------received community from R4

-----------R1 is not attaching the community to summary prefix...

Rack1R1#sh ip bgp 112.0.0.0/5
BGP routing table entry for 112.0.0.0/5, version 26
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
        1    2
  {54,50,60}, (aggregated by 100 150.1.1.1)
    0.0.0.0 from 0.0.0.0 (150.1.1.1)
      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best
      Community: 54 <------------------------------------------------------------------No community attached
      DMZ-Link Bw 12500 kbytes

===============R1 CONFIG_==========================

router bgp 100
 no synchronization
 bgp log-neighbor-changes
 bgp dmzlink-bw
 aggregate-address 112.0.0.0 248.0.0.0 as-set summary-only
 neighbor 155.1.13.3 remote-as 200
 neighbor 155.1.13.3 send-community both
 neighbor 155.1.13.3 soft-reconfiguration inbound
 neighbor 155.1.146.4 remote-as 100
 neighbor 155.1.146.4 route-reflector-client
 neighbor 155.1.146.4 send-community both
 no auto-summary
!

-================R4 CONFIG================

router bgp 100
 no synchronization
 bgp log-neighbor-changes
 bgp dmzlink-bw
 network 155.1.146.0 mask 255.255.255.0
 network 204.12.1.0
 aggregate-address 155.1.0.0 255.255.0.0 summary-only
 redistribute connected route-map ABC
 neighbor 155.1.45.5 remote-as 200
 neighbor 155.1.45.5 send-community both
 neighbor 155.1.146.1 remote-as 100
 neighbor 155.1.146.1 send-community both
 neighbor 155.1.146.1 soft-reconfiguration inbound
 neighbor 204.12.1.254 remote-as 54
 neighbor 204.12.1.254 soft-reconfiguration inbound
 neighbor 204.12.1.254 route-map ATT in
 neighbor 204.12.1.254 dmzlink-bw
 no auto-summary

Rack1R4#sh route-map ATT
route-map ATT, permit, sequence 10
  Match clauses:
    ip address prefix-lists: ATT
  Set clauses:
    community no-export
  Policy routing matches: 0 packets, 0 bytes
route-map ATT, permit, sequence 20
  Match clauses:
  Set clauses:
  Policy routing matches: 0 packets, 0 bytes
Rack1R4#sh ip pref
Rack1R4#sh ip prefix-list ATT
ip prefix-list ATT: 1 entries
   seq 5 permit 112.0.0.0/8

 


Please confirm the understanding.

 

Regards

Ganpat

Comments

  • one more observation===

     

    ON R1 112.0.0.0/8 is best from R6....

    Rack1R1#sh ip bgp 112.0.0.0 255.0.0.0
    BGP routing table entry for 112.0.0.0/8, version 27
    Paths: (2 available, best #1, table Default-IP-Routing-Table, Advertisements sup                                                                                        pressed by an aggregate.)
      Not advertised to any peer
      54 50 60, (Received from a RR-client), (received & used)
        54.1.1.254 from 155.1.146.6 (150.1.6.6)
          Origin IGP, metric 0, localpref 100, valid, internal, best
          DMZ-Link Bw 193 kbytes
      54 50 60, (Received from a RR-client)
        204.12.1.254 from 155.1.146.4 (223.255.255.255)
          Origin IGP, metric 0, localpref 100, valid, internal
          Community: no-export
          DMZ-Link Bw 12500 kbytes

    If i remove the R6 nei on R1 then its attaching the community.

    Rack1R1#sh ip bgp 112.0.0.0 248.0.0.0
    BGP routing table entry for 112.0.0.0/5, version 51
    Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)
      Advertised to update-groups:
            1
      {54,50,60}, (aggregated by 100 150.1.1.1)
        0.0.0.0 from 0.0.0.0 (150.1.1.1)
          Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best
          Community: 54 no-export

    ---------------------------------------------------------------------

     

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