BGP community configuration advice

[paul amaral]

Hi, I have setup some BGP communities for my customers to change the local_pref which are working however I wanted to know if the following config would work in reference to below config.

Basically I setup a community called 6666 that will backhole a prefix of the customers desire, basically sending it to null0 on my router. Is this the best way to do this ?

route-map customer-communities, permit, sequence 60
  Match clauses:
    community (community-list filter): 6
  Set clauses:
    ip next-hop 6.6.6.6
  Policy routing matches: 0 packets, 0 bytes

also I would like the customer to do AS prepend via bgp communities but im confused on what AS to prepend or the best away to go about this. I'm assuming that I should be prepending the customer AS and no mine correct? so in order to achieve this I have the following setup, note that im using prepend last-as because I think i will need to prepend their AS# and no mine and this will achieve this.

route-map customer-communities, permit, sequence 40
  Match clauses:
    community (community-list filter): 4
  Set clauses:
    as-path prepend last-as 2
  Policy routing matches: 0 packets, 0 bytes
route-map customer-communities, permit, sequence 50
  Match clauses:
    community (community-list filter): 5
  Set clauses:
    as-path prepend last-as 4
  Policy routing matches: 0 packets, 0 bytes

TIA, Paul

[Philip D'Ath]

I don't think I would give customers the ability to random black hole prefixes.  Very dangerous.

You could just as easily create a static NULL route yourself, and redistribute that static into BGP.

On the customers CPE, a typical path prepend might look like:

route-map customer-out permit 10
  set as-path prepend <ASN> <ASN> <ASN> <ASN>

router bgp <ASN>
  neighbor a.b.c.d route-map customer-out out

[paul amaral]

point take on the black hole idea. however i know how to set AS prepend from the customers view using a route-map like you have above. What i want is the customer to just send a predefined community tag that will prepend on my router, the ISP router. 

i not sure if this will prepend the customer AS#, im assuming that is what I want to do, prepend the customer AS and not mine and that the set   as-path prepend last-as  does this.

route-map customer-communities, permit, sequence 50
  Match clauses:
    community (community-list filter): 5
  Set clauses:
    as-path prepend last-as 4
  Policy routing matches: 0 packets, 0 bytes

[Philip D'Ath]

Wouldn't using MED be much simpler in this case?

I don't know if the route-map given will work or not.

[paul amaral]

Philip, im going with the original config posts, i think its going to work as for the remote blackhole, there is an ip prefix-list in place that will only allow customers to blackhole their own subnets.