What is ORF does ?, in simple word I can explaint about ORF, that is the ability of BGP Neighbors to tell each others what Neighboor prefix they want to transfer to it’s neighboor.
when we used ORF on our BGP topology it’s will save Demarcs point Traffict between R1 and R2, rather than we use only filtering it’s consume more traffict because the full route prefix already been sent to neighbor and it’s filtered from it’d policy.
For Example :
R1 and R2 are BGP Neighboor, R2 just interest for prefix 1.1.1.0/24 from R1 to be transfer to R2. R1 responds its request so R1 will just advertise 1.1.1.0/24 to R2, R1 doesnt bother 7.7.7.0/24 and the others tables to adv to R1.
ON LAB:
R1
==========
R1 Route Table :
R1#show ip bgp
BGP table version is 51, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.0/24 0.0.0.0 0 32768 i
*> 2.2.2.0/24 172.16.12.2 0 0 22 i
*> 3.3.3.0/24 172.16.13.3 0 0 3 i
*> 4.4.4.0/24 172.16.13.3 0 3 i
*> 5.5.5.0/24 172.16.13.3 0 3 i
*> 6.6.6.0/24 172.16.13.3 0 3 i
*> 7.7.7.0/24 172.16.13.3 0 3 i
*> 8.0.0.0 172.16.13.3 0 0 3 i
*> 9.9.9.0/24 172.16.13.3 0 3 89 i
*> 23.0.0.64/29 172.16.13.3 0 0 3 i
*> 23.0.0.64/26 172.16.13.3 0 0 3 i
*> 23.0.0.72/29 172.16.13.3 0 3 i
*> 23.0.0.80/29 172.16.13.3 0 3 i
*> 23.0.0.88/29 172.16.13.3 0 3 i
*> 23.0.0.96/29 172.16.13.3 0 3 i
*> 123.2.0.0/21 172.16.12.2 0 0 22 i
*> 124.2.0.0/18 172.16.12.2 0 0 22 i
Network Next Hop Metric LocPrf Weight Path
*> 125.2.0.0/24 172.16.12.2 0 0 22 i
R1# conf t
R1(config)#router bgp 11
R1(config-router)#neighbor 172.16.12.2 capability orf prefix-list both
note orf can be Receive/Send/both direction orf capability in this lab I use BOTH
R2
========
R2(config-router)#neighbor 172.16.12.1 capability orf prefix-list both
R2(config-router)#neighbor 172.16.12.1 prefix-list ORF_TEST in
R2(config-router)# exit
R2 (config)#ip prefix-list ORF_TEST seq 10 permit 1.1.1.0/24
R2 (config)#ip prefix-list ORF_TEST seq 20 permit 2.2.2.0/24
R2 (config)#ip prefix-list ORF_TEST seq 30 permit 3.3.3.0/24
R2 (config)#ip prefix-list ORF_TEST seq 40 permit 7.7.7.0/24
R2 (config)#R2(config)#do sh ip bgp
BGP table version is 8, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.0/24 172.16.12.1 0 0 11 i
*> 2.2.2.0/24 0.0.0.0 0 32768 i
*> 3.3.3.0/24 172.16.12.1 0 11 3 i
*> 7.7.7.0/24 172.16.12.1 0 11 3 i
*> 123.2.0.0/21 0.0.0.0 0 32768 i
*> 124.2.0.0/18 0.0.0.0 0 32768 i
*> 125.2.0.0/24 0.0.0.0 0 32768 i
note: Routing table on R2 only Requested routing table from R1
R1#sh ip bgp neighbors 172.16.12.2 | i ORF
Outbound Route Filter (ORF) type (128) Prefix-list:
Outbound Route Filter (ORF): received (4 entries)
ORF prefix-list: 10 n/a
from R1 its was Received 4 entries ORF Request from R2