Configuring Bgp Decision Attributes - Cisco 3845 - Security Bundle Router Software Manual

Configuring BGP
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 29-10 Advantages and Disadvantages of Hard and Soft Resets
Type of Reset
Hard reset
Outbound soft reset
Dynamic inbound soft reset Does not clear the BGP session and cache
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:
Command
Step 1
show ip bgp neighbors
Step 2 clear ip bgp {* | address |
peer-group-name}
Step 3
clear ip bgp {* | address |
peer-group-name} soft out
Step 4
show ip bgp
show ip bgp neighbors

Configuring BGP Decision Attributes

When a BGP speaker receives updates from multiple autonomous systems that describe different paths
to the same destination, it must choose the single best path for reaching that destination. The decision is
based on the value of attributes that the update contains and other BGP-configurable factors. The
selected path is entered into the BGP routing table and propagated to its neighbors.
When a BGP peer learns two EBGP paths for a prefix from a neighboring AS, it chooses the best path
and inserts that path in the IP routing table. If BGP multipath support is enabled and the EBGP paths are
learned from the same neighboring autonomous systems, multiple paths are installed in the IP routing
Cisco ME 3800X and 3600X Switch Software Configuration Guide
29-48
Advantages
No memory overhead
No configuration, no storing of routing table
updates
Does not require storing of routing table updates
and has no memory overhead
Purpose
Display whether a neighbor supports the route refresh capability. When supported,
this message appears for the router:
Received route refresh capability from peer.
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.
(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.
Verify the reset by checking information about the routing table and about BGP
neighbors.
Chapter 29 Configuring IP Unicast Routing
Disadvantages
The prefixes in the BGP, IP, and FIB tables
provided by the neighbor are lost. Not
recommended.
Does not reset inbound routing table updates.
Both BGP routers must support the route
refresh capability.
OL-23400-01