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Regarding BGP attribute-map configuration

Unanswered Question
Feb 19th, 2012
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R1 AS100--------L2SWITCH---------R4 AS100
                              |
                              |
                              |
                    R1( AS100)
                             |
                             |
                             |
                    R3 (AS200)


-------R4 is sending to R1 via ibgp


112.0.0.0/8 with "No-export" comm
113.0.0.0/8 No eommunity


R1#sh ip bgp 112.0.0.0/8
BGP routing table entry for 112.0.0.0/8, version 5
Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer, Advertisements suppressed by an aggregate.)
Flag: 0x820
  Not advertised to any peer
  Local, (Received from a RR-client)
    155.1.146.4 from 155.1.146.4 (113.0.0.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      Community: no-export <-----------------------------------------


Router R1 is generating summary route 112.0.0.0 248.0.0.0

router bgp 100
no synchronization
bgp log-neighbor-changes
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 155.1.146.4 remote-as 100
neighbor 155.1.146.4 route-reflector-client
neighbor 155.1.146.4 send-community both


R1#sh ip bgp 112.0.0.0/5
BGP routing table entry for 112.0.0.0/5, version 10
Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)
Flag: 0x820
  Advertised to update-groups:
     1          2
  Local, (aggregated by 100 155.1.146.1)
    0.0.0.0 from 0.0.0.0 (155.1.146.1)
      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best
      Community: no-export<------------------------------Community attached to summary route as specific route is carrying the same community


Now i want to remove the "no-export" community from the summary route 112.0.0.0/5.

so i used attribute-map to remove the "no-export" community

router bgp 100
no synchronization
bgp log-neighbor-changes
aggregate-address 112.0.0.0 248.0.0.0 as-set summary-only attribute-map ATT


sh route-map ATT
route-map ATT, permit, sequence 10
  Match clauses:--------------------------> No match statement.
  Set clauses:
    community none
  Policy routing matches: 0 packets, 0 bytes


R1#sh ip bgp 112.0.0.0/5
BGP routing table entry for 112.0.0.0/5, version 13
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Flag: 0x880
  Advertised to update-groups:
     1          2
  Local, (aggregated by 100 155.1.146.1)
    0.0.0.0 from 0.0.0.0 (155.1.146.1)
      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best <----Commnity removed


Till here everything is looking fine.

Now if i match the prefix 112.0.0.0/5 in attribute-map its not removing the community of the route.


R1#sh route-map ATT
route-map ATT, permit, sequence 10
  Match clauses:
    ip address prefix-lists: ATT
  Set clauses:
    community none
  Policy routing matches: 0 packets, 0 bytes
route-map ATT, permit, sequence 20
  Match clauses:
  Set clauses:
  Policy routing matches: 0 packets, 0 bytes


R1#sh ip prefix-list ATT
ip prefix-list ATT: 1 entries
   seq 5 permit 112.0.0.0/5

router bgp 100
no synchronization
bgp log-neighbor-changes
aggregate-address 112.0.0.0 248.0.0.0 as-set summary-only attribute-map ATT
neighbor 155.1.13.3 remote-as 200
neighbor 155.1.13.3 send-community both
neighbor 155.1.146.4 remote-as 100
neighbor 155.1.146.4 route-reflector-client
neighbor 155.1.146.4 send-community both

R1#sh ip bgp 112.0.0.0/5
BGP routing table entry for 112.0.0.0/5, version 4
Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)
  Advertised to update-groups:
     1
  Local, (aggregated by 100 155.1.146.1)
    0.0.0.0 from 0.0.0.0 (155.1.146.1)
      Origin IGP, localpref 100, weight 32768, valid, aggregated, local, best
      Community: no-export <------------------------------Community present in route


Want to know is matching crateria is not allowed OR not working in this senario.


This just to identify the reason.


Please suggest.

/Ganapt

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Dan-Ciprian Cicioiu Sun, 02/19/2012 - 02:49
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Hi ,


I do not belive that match statements are permited on attribute map. This attribute map changes the attributes of the aggregate, so I do not see any logic behind using match.


Dan

csco10851021 Sun, 02/19/2012 - 03:30
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Hi Dan,


I am not seeing logic in this however as per configuration its should macth the prefix 112.0.0.0/5


!

router bgp 100

no synchronization

bgp log-neighbor-changes

aggregate-address 112.0.0.0 248.0.0.0 as-set summary-only attribute-map ATT

!

ip prefix-list ATT seq 5 permit 112.0.0.0/5

!

route-map ATT permit 10

match ip address prefix-list ATT

set community none

!

route-map ATT permit 20!
!

/Ganpat

Dan-Ciprian Cicioiu Sun, 02/19/2012 - 05:09
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Hi ,


As per config guidelines , if you see the suppress-map and advertise-map have the explicit support of match statements - still limited to ACL and as-path acl - but the attribute-map does not have an explicit support of match. The desciption tells that : "An attribute map route map can be created to change the aggregate attributes." So I will stick to my first impresion that attribute-map does not support match statements.




#

Using the suppress-map keyword creates the aggregate route but suppresses advertisement of specified routes. You can use the match clauses of route maps to selectively suppress some more-specific routes of the aggregate and leave others unsuppressed. IP access lists and autonomous system path access lists match clauses are supported.

#

Using the advertise-map keyword selects specific routes that will be used to build different components of the aggregate route, such as AS_SET or community. This form of theaggregate-address command is useful when the components of an aggregate are in separate autonomous systems and you want to create an aggregate with AS_SET, and advertise it back to some of the same autonomous systems. You must remember to omit the specific autonomous system numbers from the AS_SET to prevent the aggregate from being dropped by the BGP loop detection mechanism at the receiving router. IP access lists and autonomous system path access lists match clauses are supported.

#

Using the attribute-map keyword allows attributes of the aggregate route to be changed. This form of the aggregate-address command is useful when one of the routes forming the AS_SET is configured with an attribute such as the community no-export attribute, which would prevent the aggregate route from being exported. An attribute map route map can be created to change the aggregate attributes.



Dan

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