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
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