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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 32 Configuring IP Unicast Routing
Configuring BGP
Managing Routing Policy Changes
Routing policies for a peer include all the configurations that might affect inbound or outbound routing
table updates. When you have defined two routers as BGP neighbors, they form a BGP connection and
exchange routing information. If you later change a BGP filter, weight, distance, version, or timer, or
make a similar configuration change, you must reset the BGP sessions so that the configuration changes
take effect.
There are two types of reset, hard reset and soft reset. Cisco IOS Releases 12.1 and later support a soft
reset without any prior configuration. To use a 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. A 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.
• When soft reset generates inbound updates from a neighbor, it is called dynamic inbound soft reset.
• When soft reset sends a set of updates to a neighbor, it is called outbound soft reset.
A soft inbound reset causes the new inbound policy to take effect. A soft outbound reset causes the new
local outbound policy to take effect without resetting the BGP session. As a new set of updates is sent
during outbound policy reset, a new inbound policy can also take effect.
Table 32-10 lists the advantages and disadvantages hard reset and soft reset.
Beginning in privileged EXEC mode, follow these steps to learn if a BGP peer supports the route refresh
capability and to reset the BGP session:
Table 32-10 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 FIB tables
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 and cache
Does not require storing of routing table updates
and has no memory overhead
Both BGP routers must support the route
refresh capability (in Cisco IOS Release 12.1
and later).
Command Purpose
Step 1
show ip bgp neighbors Display whether a neighbor supports the route refresh capability. When supported,
this message appears for the router:
Received route refresh capability from peer.
Step 2
clear ip bgp {* | address |
peer-group-name}
Reset the routing table on the specified connection.
• Enter an asterisk (*) to specify that all connections be reset.
• Enter an IP address to specify the connection to be reset.
• Enter a peer group name to reset the peer group.