Route Refresh

A new feature available from IOS Software Release 12.0(5)S is route refresh (documented in RFC 2918). The concept is similar to soft reconfiguration, but this is a capability shared between two BGP speakers (as opposed to soft reconfiguration, which is configured on the local router only) and it is negotiated automatically at the time the BGP session is brought up. To find out whether route refresh is supported, check the BGP neighbor using the following command:

alpha>sh ip bgp neighbors 192.168.4.130

BGP neighbor is 192.168.4.130, remote AS 2830, external link Index 1, Offset 0, Mask 0x2 Community attribute sent to this neighbor BGP version 4, remote router ID 192.168.11.1 BGP state = Established, table version = 207, up for 16w1d Last read 00:00:01, last send 00:00:08 Hold time 30, keepalive interval 10 seconds

Configured hold time is 30, keepalive interval is 10 seconds Default information originate

Unicast default sent, multicast default not sent Neighbor NLRI negotiation:

Configured for unicast routes only Peer negotiated unicast routes only Exchanging unicast routes only Received route refresh capability(new) from peer

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Minimum time between advertisement runs is 30 seconds Received 1648106 messages, 0 notifications, 0 in queue Sent 1648064 messages, 0 notifications, 0 in queue Prefix advertised 125, suppressed 1, withdrawn 66 Route refresh request: received 0, sent 1 Connections established 2; dropped 1 Last reset 16w1d, due to Peer closed the session Number of unicast/multicast prefixes received 3/0

The portion highlighted with ^^^^^^^ shows that the route refresh capability has been negotiated between the two BGP neighbors. The "(new)" in the capability statement indicates that the routers support the IANA-assigned route refresh capability code (which has a value of 2, described in RFC 2918) rather than the Cisco-specific code when the feature first was developed by Cisco (which would show up as "(old)"). (All the IANA-assigned BGP capability codes are listed at http://www.iana.org/assignments/capability-codes.)

If the local router requires a fresh view of the routing table, it can send a route-refresh request to the neighboring BGP peer. This would be required, for example, when the inbound routing policy has been changed. Upon receipt of the route-refresh request, the remote router would send its list of prefixes to the requesting router. The route refresh capability requires no extra memory on the local router. Where the capability exists between speakers, it is strongly recommended that this is chosen over soft reconfiguration (because the latter requires more memory to store the inbound prefixes received from the remote peer). To request a route refresh inbound, use this command:

clear ip bgp [neighbor] in

No other configuration is required. To reset the BGP session outbound using route refresh, simply use this command:

clear ip bgp [neighbor] out

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