IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3850 Switches)
BGP 4 Soft Configuration
BGP 4 Soft Configuration
Last Updated: November 21, 2012
BGP4 soft configuration allows BGP4 policies to be configured and activated without clearing the BGP session, hence without invalidating the forwarding cache.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
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Information About BGP 4 Soft Configuration
BGP Session Reset
Whenever the routing policy changes due to a configuration change, BGP peering sessions must be reset by using the clear ip bgp command. Cisco software supports the following three mechanisms to reset BGP peering sessions:
Received route refresh capability from peer.
The bgp soft-reconfig-backup command was introduced to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.
How to Configure BGP 4 Soft Configuration
Configuring Inbound Soft Reconfiguration When Route Refresh Capability Is Missing
Perform this task to configure inbound soft reconfiguration using the bgp soft-reconfig-backup command for BGP peers that do not support the route refresh capability. BGP peers that support the route refresh capability are unaffected by the configuration of this command. Note that the memory requirements for storing the inbound update information can become quite large.
The following partial output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.2.1. This peer supports route refresh.
BGP neighbor is 192.168.1.2, remote AS 40000, external link Neighbor capabilities: Route refresh: advertised and received(new)
The following partial output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.3.2. This peer does not support route refresh so the soft-reconfig inbound paths for BGP peer 192.168.3.2 will be stored because there is no other way to update any inbound policy updates.
BGP neighbor is 192.168.3.2, remote AS 50000, external link Neighbor capabilities: Route refresh: advertised
The following sample output from the show ip bgp command shows the entry for the network 172.17.1.0. Both BGP peers are advertising 172.17.1.0/24, but only the received-only path is stored for 192.168.3.2.
BGP routing table entry for 172.17.1.0/24, version 11 Paths: (3 available, best #3, table Default-IP-Routing-Table, RIB-failure(4)) Flag: 0x820 Advertised to update-groups: 1 50000 192.168.3.2 from 192.168.3.2 (172.17.1.0) Origin incomplete, metric 0, localpref 200, valid, external 50000, (received-only) 192.168.3.2 from 192.168.3.2 (172.17.1.0) Origin incomplete, metric 0, localpref 100, valid, external 40000 192.168.1.2 from 192.168.1.2 (172.16.1.0) Origin incomplete, metric 0, localpref 200, valid, external, best
Configuration Examples for BGP 4 Soft Configuration
Examples: BGP Soft Reset
Example: Dynamic Inbound Soft Reset
The following example shows the command used to initiate a dynamic soft reconfiguration in the BGP peer 192.168.1.1. This command requires that the peer support the route refresh capability.
clear ip bgp 192.168.1.1 soft in
Example: Inbound Soft Reset Using Stored Information
The following example shows how to enable inbound soft reconfiguration for the neighbor 192.168.1.1. All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is performed later, the stored information will be used to generate a new set of inbound updates.
router bgp 100 neighbor 192.168.1.1 remote-as 200 neighbor 192.168.1.1 soft-reconfiguration inbound
The following example clears the session with the neighbor 192.168.1.1:
clear ip bgp 192.168.1.1 soft in
Feature Information for BGP 4 Soft Configuration
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.
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