Administrator Guide

When two neighbors, congured with dierent keepalive and holdtime values, negotiate for new values, the resulting values
are as follows:
• the lower of the holdtime values is the new holdtime value, and
• whichever is the lower value; one-third of the new holdtime value, or the congured keepalive value is the new
keepalive value.
• Congure timer values for a BGP neighbor or peer group.
CONFIG-ROUTER-BGP mode
neighbors {ip-address | peer-group-name} timers keepalive holdtime
– keepalive: the range is from 1 to 65535. Time interval, in seconds, between keepalive messages sent to the neighbor
routers. The default is 60 seconds.
– holdtime: the range is from 3 to 65536. Time interval, in seconds, between the last keepalive message and declaring the
router dead. The default is 180 seconds.
• Congure timer values for all neighbors.
CONFIG-ROUTER-BGP mode
timers bgp keepalive holdtime
– keepalive: the range is from 1 to 65535. Time interval, in seconds, between keepalive messages sent to the neighbor
routers. The default is 60 seconds.
– holdtime: the range is from 3 to 65536. Time interval, in seconds, between the last keepalive message and declaring the
router dead. The default is 180 seconds.
To view non-default values, use the show config command in CONFIGURATION ROUTER BGP mode or the show running-
config bgp
command in EXEC Privilege mode.
Enabling BGP Neighbor Soft-Reconguration
BGP soft-reconguration allows for faster and easier route changing.
Changing routing policies typically requires a reset of BGP sessions (the TCP connection) for the policies to take eect. Such resets
cause undue interruption to trac due to hard reset of the BGP cache and the time it takes to re-establish the session. BGP soft
recong allows for policies to be applied to a session without clearing the BGP Session. Soft-recong can be done on a per-neighbor
basis and can either be inbound or outbound.
BGP soft-reconguration clears the policies without resetting the TCP connection.
To reset a BGP connection using BGP soft reconguration, use the clear ip bgp command in EXEC Privilege mode at the
system prompt.
When you enable soft-reconguration for a neighbor and you execute the clear ip bgp soft in command, the update
database stored in the router is replayed and updates are reevaluated. With this command, the replay and update process is triggered
only if a route-refresh request is not negotiated with the peer. If the request is indeed negotiated (after execution of
clear ip
bgp soft in), BGP sends a route-refresh request to the neighbor and receives all of the peer’s updates.
To use soft reconguration (or soft reset) without preconguration, both BGP peers must support the soft route refresh capability,
which is advertised in the open message sent when the peers establish a TCP session.
To determine whether a BGP router supports this capability, use the show ip bgp neighbors command. If a router supports
the route refresh capability, the following message displays:
Received route refresh capability from peer.
If you specify a BGP peer group by using the peer-group-name argument, all members of the peer group inherit the
characteristic congured with this command.
• Clear all information or only specic details.
EXEC Privilege mode
192
Border Gateway Protocol IPv4 (BGPv4)