ORF short notes


ORF is a method of limiting routing updates sent from router B to router A by creating a prefix-list on router A and sending it over to router B so that router B applies it outbound towards router A. Why? it is always better to limit routing updates outbound than inbound on the other end because this saves bandwidth.

  1. enable capability on router B
    ROUTER B: neighbor capability orf prefix-list both
  2. create a loopback on router B and advertise it into BGP

int loop22

ip addr

router bgp 100

network mask

3. Enable capability on router A


ROUTER A: neighbor capability orf prefix-list both

4. Create a prefix list that denies some prefix and apply it INBOUND (yes, inbound!) towards router B

neighbor prefix-list dontsendloopback22 in

ip prefix-list dontsendloopback22 deny

ip prefix-list dontsendloopback22 permit le 32

5. Soft clear BGP for the prefix filter.

clear ip bgp soft in prefix-filter

6. Watch the filter being applied on router B:

RouterB#show ip bgp neighbors received prefix-filter
Address family: IPv4 Unicast
ip prefix-list 2 entries
seq 5 deny
seq 10 permit le 32



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