BGP route refresh is an optional BGP capability that allows a BGP router to request retransmission of BGP routes from a neighbor

The soft-reconfiguration inbound feature consumes large volumes of memory in the Internet environment. The number of routes that can be received from a peer router on the Internet is so large that it is not feasible to store an extra copy.

The only reason for making the extra copy is to be able to replay the data through the new routing policy without tearing down the session and re-establishing it.

What is needed is a mechanism to ask the neighbor router to do a "clear soft outbound." If this were possible, the extra copy would not be needed. The neighboring router, of course, has its own copy in its BGP table, which it could resend to the local router whenever it is signaled to do so.

There is no such mechanism in standard BGP, but there is an optional BGP capability that allows one router to request a refresh from its neighbor: route refresh.

3-114 Configuring BGP on Cisco Routers (BGP) v3.2

The table compares the various methods of BGP session reset, stating the advantages and disadvantages of each.

Type of Reset

Advantages

Disadvantages

Hard reset

No memory overhead.

The prefixes in the BGP, IP, and FIB tables that are provided by the neighbor are lost.

Not recommended.

Outbound soft reset

No configuration, no storing of routing table updates.

Does not reset inbound routing table updates.

Dynamic inbound soft reset

Does not clear the BGP session or cache.

Does not require storing of routing table updates, and has no memory overhead.

Both BGP routers must support the route refresh capability (Cisco IOS Software Release 12.1 and later releases).

Configured inbound soft reset (uses the neighbor soft-reconfiguration command)

Can be used when both BGP routers do not support the automatic route refresh capability.

Requires preconfiguration.

Stores all received (inbound) routing policy updates without modification, and is thus memory-intensive.

Recommended only when absolutely necessary.

© 2005, Cisco Systems, Inc. Route Selection Using Policy Controls 3-115

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