filtering a range of RTs by use of expanded extended community

[gristanovic]

Hi,

I am trying to test a configuration that uses expanded extended community lists, the aim of the config is to block out a range of RTs. 

;

The range I need blocked is from RT

I was planning to use an expanded extended list and a route map, a route map applied inbound on a bgp router (this router is a border router and my aim is to block the routes as they arrive from the far end bgp peer).

I have configured following, but no luck

ip extcommunity-list 155 deny ^RT:xxxx:[0-9]{1,7}$

route-map Gordana-inbound-to-uk deny 10
match extcommunity 155

The above route map applied on ebgp neighbour inbound

I have tested the regex in an on line regex test tool with relevant test RTs (i.e all numbers below 10000000 , RTs that have 7 digits were false as required)

My production routes wil have a number of RTs attached, e.g example test route below

65516-BGP-BR-1#show ip bgp vpnv4 rd xxxx:1880 4.4.4.4
BGP routing table entry for xxxx:1880:4.4.4.4/32, version 16620786
Paths: (2 available, best #1, table NULL)
  Advertised to non peer-group peers:
  x.x.x.x
  Local
    x.x.x.x (metric 31410) from x.x.x.x
      Origin IGP, localpref 100, valid, confed-internal, best
      Extended Community: RT:xxxx:5 RT:xxxx:666 RT:xxxx:18800 RT:xxxx:20000115
      Originator: x.x.x.x, Cluster list: x.x.x.x
  Local
    x.x.x.x (metric 31410) from x.x.x.x
      Origin IGP, localpref 100, valid, confed-internal
      Extended Community: RT:xxxx:5 RT:xxxx:666 RT:xxxx:18800 RT:xxxx:20000115
      Originator: x.x.x.x, Cluster list: x.x.x.x, x.x.x.x
65516-BGP-BR-1

So in summary my questions are

1) is the above regex correct for blocking out a range of RTs from say RT:xxxx:0 to RT:xxxx:9999999
2) are you aware of any show ip bgp vpnv4 command i can use to confirm that the above community list sytax is correct?
3) regardinf use of extended community list in a route map, in order to deny a route, do I need to use deny in both community list and route map, i tried a number of permutations but no change.  I have also tried a number of permutations of regex, i.e. with letters "RT:" included , with and without ^ and $ but no luck.

Thanks.

Gordana

[Harold Ritter]

Hi Gordana,

1. The syntax {n,m} is actually not supported by IOS. You could meet the requirement with an extended community list similar to this:

ip extcommunity-list 155 permit ^RT:1:[0-9][0-9]?[0-9]?[0-9]?[0-9]?[0-9]?[0-9]?$

2. "show bgp vpnv4 unicast all extcommunity-list xxx" can help you with this.

3. To meet the requirement, you need to permit in the extcommunity-list and deny in the route-map

route-map test deny 10

match extcommunity 155

route-map test permit 20

!

ip extcommunity-list 155 permit ^RT:1:[0-9][0-9]?[0-9]?[0-9]?[0-9]?[0-9]?[0-9]?$

Regards