user manual

42-51
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 42 Configuring IP Unicast Routing
Configuring BGP
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 tak
e 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 42-10 lists the a
dvantages 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:
Ta ble 42-10 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
pro
vided by the neighbor are lost. Not
recommended.
Outbound soft reset No configuration, no storing of routing table
u
pdates
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
re
fresh 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.
Step 3
clear ip bgp {* | address |
peer-group-name} soft out
(Optional) Perform an outbound soft reset to reset the inbound routing table on the
specified connection. Use this command if route refresh is supported.
• 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.
Step 4
show ip bgp
show ip bgp neighbors
Verify the reset by checking information about the routing table and about BGP
neighbors.