Cisco Systems 78-11741-02 Managing Routing Policy Changes, Type of Reset Advantages Disadvantages

Configuring BGP

Configuring Basic BGP Features

Managing Routing Policy Changes

Routing policies for a peer include all the configurations such as route-map, distribute-list, prefix-list, and filter-list that may impact inbound or outbound routing table updates. Whenever there is a change in the routing policy, the BGP session must be soft cleared, or soft reset, for the new policy to take effect. Performing inbound reset enables the new inbound policy to take effect. Performing outbound reset causes the new local outbound policy take effect without resetting the BGP session. As a new set of updates is sent during outbound policy reset, a new inbound policy of the neighbor can also take effect.

There are two types of reset, hard reset and soft reset. Table 8 lists their advantages and disadvantages.

Table 8	Advantages and Disadvantages of Hard and Soft Resets
Type of Reset		Advantages	Disadvantages
Hard reset		No memory overhead.	The prefixes in the BGP, IP, and
			Forwarding Information Base (FIB)
			tables provided by the neighbor are
			lost. Not recommended.
Outbound soft reset		No configuration, no storing of routing	Does not reset inbound routing table
		table updates.	updates.
		The procedure for an outbound reset is
		described in the section “Configuring
		BGP Soft Reset Using Stored Routing
		Policy Information.”
Dynamic inbound		Does not clear the BGP session and	Both BGP routers must support the
soft reset		cache.	route refresh capability (in Cisco IOS
		Does not require storing of routing	Release 12.1 and later releases).
		table updates, and has no memory
		overhead.
Configured inbound		Can be used when both BGP routers do	Requires preconfiguration.
soft reset (uses the		not support the automatic route refresh	Stores all received (inbound) routing
neighbor		capability.	policy updates without modification;
soft-reconfiguration
			is memory-intensive.
router configuration
			Recommended only when absolutely
command)
			necessary, such as when both BGP
			routers do not support the automatic
			route refresh capability.

Once you have defined two routers to be BGP neighbors, they will form a BGP connection and exchange routing information. If you subsequently change a BGP filter, weight, distance, version, or timer, or make a similar configuration change, you must reset BGP connections for the configuration change to take effect.

Cisco IOS IP Configuration Guide

IPC-298