Cisco Systems 78-11741-02 manual Resetting a Router Using BGP Dynamic Inbound Soft Reset, IPC-299

Configuring BGP

Configuring Basic BGP Features

A soft reset updates the routing table for inbound and outbound routing updates. Cisco IOS software Release 12.1 and later releases support soft reset without any prior configuration. This soft reset allows the dynamic exchange of route refresh requests and routing information between BGP routers, and the subsequent re-advertisement of the respective outbound routing table. There are two types of soft reset:

•When soft reset is used to generate inbound updates from a neighbor, it is called dynamic inbound soft reset.

•When soft reset is used to send a new set of updates to a neighbor, it is called outbound soft reset.

To use soft reset without preconfiguration, 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. Routers running Cisco IOS software releases prior to Release 12.1 do not support the route refresh capability and must clear the BGP session using the neighbor soft-reconfigurationrouter configuration command, described in “Configuring BGP Soft Reset Using Stored Routing Policy Information.” Clearing the BGP session in this way will have a negative impact upon network operations and should only be used as a last resort.

Resetting a Router Using BGP Dynamic Inbound Soft Reset

If both the local BGP router and the neighbor router support the route refresh capability, you can perform a dynamic soft inbound reset. This type of reset has the following advantages over a soft inbound reset using stored routing update information:

•Does not require preconfiguration

•Does not require additional memory for storing routing update information

To determine whether a router supports the route refresh capability, use the show ip bgp neighbors command in EXEC mode:

Command	Purpose
Router# show ip bgp neighbors	Displays whether a neighbor supports the route refresh capability.
ip-address	If the specified router supports the route refresh capability, the following
	message is displayed: Received route refresh capability from peer.

If all the BGP routers support the route refresh capability, you can use the dynamic soft reset method for resetting the inbound routing table. To perform a dynamic soft reset of the inbound routing table, use the following command in EXEC mode:

Command	Purpose
Router# clear ip bgp {*	Performs a dynamic soft reset on the connection specified in the command.
neighbor-address peer-group-name}	The neighbor-addressargument specifies the connection to be reset. Use the
soft in
	* keyword to specify that all connections be reset.

See the “BGP Soft Reset Examples” section at the end of this chapter for examples of both types of BGP soft resets.

Cisco IOS IP Configuration Guide

IPC-299