BPG route filtering

[Michael Moore]

Hello all,

Question. I have worked at many compaines and I always see route filtering performed the same way when using BGPv4. Prefix list. Why do admins use this method. Dont route-maps/distribute list perform the same function ?

Look forward to the great answers !

[smehrnia]

Hi Michael,

we use prefix lists because it is capable of storing ip address information in a efficient structure (Permit/Deny), capable of defining one ip address or a range of prefixes. it is sequenced so we can insert different entries in one list and then simply bind it to a bgp neighbor.

you can also use access-lists for bgp route filtering but its not as effective as prefix lists.

route-maps themselvs use an ACL or a Prefix list for their match clause, you never want to wrap a thing into another thing and give it to your router, do u? distribute list is for IGP use.

are you THE Michael Moore? jk

plz Rate if it helped.

Soroush.

[Michael Moore]

lol !  I am that Michael Moore. I decided film making was much to hard work for me

Thank you on answering my question. Distribute list is only for IGPs and cannot be incorporated into EGP ?

So the only reason why we choose prefix-list really is based on organization. Everything else route-maps can do but the function is albeit differnt (match criteria and modify (set) packets).

In the case of BGP I often see it this way. Prefix-list created. Route-map created that references the prefix-list. Finally in the BGP neighbor statement we are filtering traffic based on that route map which is based on the prefix list. Does that make sense ? If so then are we not wrapping a thing into another thing ?