We currently have 2 peerings (BGP)our MPLS provider at our Primary and our secondary data centre. There is a layer 2 pipe between the Primary and the secondary site. The primary has a different AS number and the secondary has a different AS number. The ISP has the same AS number at both primary and secondary connections and run ibgp between their routers. We have mutual redistribution between our IGP (ospf) and BGP.
ISP A------ Primary data centre (AS B)
]
ISP A -----Secondary Data centre (AS C)
As we have mutual redistribution, The routes that we redistribute at the Primary data centre are being learned by BGP at our secondary Data centre. Now I know that we have to use prefix list to control what networks we can accept from our provider and that should filter out any IGP routes that were redistribute at either of the Data centres. We should be looking to redesign the BGP so that we do not advertise 2 different AS into our provider. This will be implemented in the future.
I would like to use BGP regular expressions to filter out any routes that has the AS of the Secondary data centre for the routes received from the peer at the Primary data centre, vice a versa. I know this is not ideal but this will help out filter any routes that were redistributed from the IGP. Going forward we will use a prefix list to filter to only accept networks that we expect from our peer
AS path Access list 10
deny _AS C
AS path Access list 30
permit .*
route-map remote-only, deny, sequence 20
Match clauses:
as-path (as-path filter): 30
neighbor x.x.x.x route-map remote-only in
Apply the above to the Primary data centre
Apply the below to the secondary data centre
AS path Access list 10
deny _ASB_
AS path Access list 30
permit .*
route-map remote-only, deny, sequence 20
Match clauses:
as-path (as-path filter): 30
neighbor x.x.x.x route-map remote-only in
Will the above BGP regular expression stop the Advertisements from the ISP A ?
CCNA R&S
