route refresh capability in bgp.

[sarahr202]

Hi everybody

Please consider the the following:

R1-----ibgp--------------R2

R1: is adentified by neighbor 199.199.199.1 by R2

R2:  is identified by neighbor 199.199.199.2 by R1

R1#show ip bgp neighbor 199.199.199.2

BGP neighbor is 199.199.199.2,  remote AS 1, internal link

  BGP version 4, remote router ID 199.199.199.2

  BGP state = Established, up for 00:05:53

  Last read 00:00:53, last write 00:00:53, hold time is 180, keepalive interval is 60 seconds

  Neighbor capabilities:

    Route refresh: advertised and received(old & new)

    Address family IPv4 Unicast: advertised and received

============================================

     What does "Route refresh: advertised and received(old & new)"   indicate?  Does it indicate R2 has refresh capability only? Does it indicate both R1 and R2 have refresh capability ?

thanks and have a great weekend

[Peter Paluch · Accepted solution]

Hi Sarah,

The "old & new" means that R2 indeed supports the Route Refresh capability. As you know, both BGP peers advertise their capabilities as a part of the OPEN message. Each capability is uniquely identified by its number. The numbers of BGP capabilities is currently maintaned by the IANA at this page:

http://www.iana.org/assignments/capability-codes/capability-codes.xml

The "old" refers to the old capability code of 128 that was used by old Cisco implementations of Route Refresh, obviously before the RFC 2918 was in place. The "new" refers to the RFC 2918 compliant capability code 2 which is used by all recent BGP implementations that support the Route Refresh according to RFC 2918.

I have attached a Wireshark capture of a BGP communication during peering establishement. In the OPEN messages from both peers, notice that the Route Refresh capability is announced twice: one using the capability code of 128 (old), another using the capability code of 2 (new).

Best regards,

Peter

[Kishore Chennupati]

RFC Guru 5 stars for that

[sarahr202]

thanks Peter.