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Re: URPF on small BGP-enabled customers?
[email protected] wrote:
At an old transit provider I was at, we had a pig of a time dealing with uRPF. It doesn't like asymmetric routing at all, which is commonplace when you've got customers homed at exchange points for one.
This is why I say there should be a feature that will work like a dynamic ACL but is fed from BGP. All the prefixes you learn from customer A via BGP are put into an automatic ACL, default is deny. Then you apply this dynamic ACL to the interface the customer is connected to. Of course it still doesn't work if you send traffic from prefixes you don't announce but for 70-80% of the cases it's a big step forward in automation. This also gets rid of any differences between ACL on the forwarding plane and on the routing protocol plane. All prefix filters are defined in BGP configuration. Forwarding layer follows and never gets out of sync again. Random example syntax: router bgp 65500 neighbor 192.168.2.2 remote-as 65501 neighbor 192.168.2.2 dynamic ACL 10001 receive #put received prefixes here neighbor 192.168.2.2 prefix-list CUST65501 ... #usual stuff #only this one is controlled ip prefix-list extended CUST65501 permit ip 172.16.0.0/16 any permit ip 10.0.0.0/8 any #ACL on interface follows BGP received prefixes interface f0/0/0 ip access-group 10001 in #same as in BGP neighbor config And Voila! Problem automagically solved. -- Andre