BGP orf

Trong mô hình mạng thực tế, router PE sẽ adver một lượng lớn prexfix sang router CE. Để tiết kiệm băng thông giữa link router PE và CE . Vì không thể được truy cập vao router PE để cấu hình filter. BGP orf là feature rất hữu dụng để filter lượng route ở PE trước khi adver sang CE. Khi cấu hình router PE sẽ chấp nhận BGP orf khi ấy feature mới được enable.

R2 filter out network 2.2.2.0/24 being advertise R1. config in R1

R1: router bgp 100  network 1.1.1.0 mask 255.255.255.0  neighbor 10.1.12.2 remote-as 100  neighbor 10.1.12.2 capability orf prefix-list both  neighbor 10.1.12.2 prefix-list ofr in  no auto-summary ! ip prefix-list ofr seq 5 deny 2.2.2.0/24 ip prefix-list ofr seq 10 permit 0.0.0.0/0 le 32

R2: router bgp 100  network 2.2.2.0 mask 255.255.255.0  neighbor 10.1.12.1 remote-as 100  neighbor 10.1.12.1 capability orf prefix-list both  no auto-summary

ORF or outbound route filtering is the technique that allows a BGP peer to “push” a filter to the remote neighbor. The neighbor then applies the prefix filter to the outbound updates sent to the peer that pushed the filter. This feature is particularly helpful in situations when BGP peers exchange large amount of BGP information. Applying filtering outbound on the remote peer instead of inbound on the local peer significantly decreases the amount of routing information send across the link. There are two types of ORF filters defined in IETF’s draft – prefix-list based and community based. Cisco IOS supports only the prefix-list ORFs