Monday, June 27, 2016

BGP Outbound Route Filtering-ORF

Enables outbound route filter (ORF) capability exchange and advertise ORF capabilities to a BGP peer,
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 where BGP peers exchange large amounts of BGP information.
Send and receive capabilities to minimize the number of BGP updates that are sent between BGP peers.

BGP peering sessions must be established, and BGP ORF capabilities must be enabled on each participating router before prefix-based ORF announcements can be sent or received.


we see all the 10.x prefixes advertised by R5 are being learned by R1




Configure both the routers Capability to send and receive the prefix 

R1(config-router)#neighbor 15.1.1.5 capability orf prefix-list send
R5(config-router)#neighbor 15.1.1.1 capability orf prefix-list receive

we will create a prefix list on R1 so that it can only receive the prefix 10.0.0.0/24 and 10.0.1.0/24

R1#
ip prefix-list ALLOW-PREFIX seq 10 permit 10.0.0.0/24
ip prefix-list ALLOW-PREFIX seq 20 permit 10.0.1.0/24

!
router bgp 123
 no synchronization
 bgp log-neighbor-changes
 network 1.1.1.0 mask 255.255.255.0
 neighbor 12.1.1.2 remote-as 123
 neighbor 12.1.1.2 next-hop-self
 neighbor 12.1.1.2 send-community
 neighbor 13.1.1.3 remote-as 123
 neighbor 13.1.1.3 next-hop-self
 neighbor 13.1.1.3 send-community
 neighbor 15.1.1.5 remote-as 500
 neighbor 15.1.1.5 capability orf prefix-list send
 neighbor 15.1.1.5 prefix-list ALLOW-PREFIX in
 no auto-summary
!






R5#show ip bgp neighbors 15.1.1.1
 For address family: IPv4 Unicast
  BGP table version 162, neighbor version 162/0
 Output queue size : 0
  Index 1, Offset 0, Mask 0x2
  1 update-group member
  Inbound soft reconfiguration allowed
  Community attribute sent to this neighbor
  AF-dependant capabilities:
    Outbound Route Filter (ORF) type (128) Prefix-list:
      Send-mode: received
      Receive-mode: advertised
  Outbound Route Filter (ORF): received (2 entries)

  Outbound path policy configured
  

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