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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
OL-13270-06
Chapter 39 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 39-10
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 39-10
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 reset all connections.
•
Enter an IP
address
to reset a specific connection.
•
Enter a peer group name to reset the peer group.
