Troubleshooting guide

Additional BGP Configuration

Router ID

The BGP interface identifies itself to neighbors with its router ID. Often this ID is the IPv4 address of the

logical interface that connects to each neighbor. However, the ID can also be the address of a loopback

interface used as the update source. A loopback interface that is the update source for BGP ensures that a

BGP session stays open even if one connection goes down. The following command specifies the router

ID:

(config-bgp)#bgp router-id <ipv4 address>

<ipv4 address> Designates the IPv4 address this router should use as its BGP router ID. IPv4 addresses

should be expressed in dotted decimal notation (for example, 10.10.10.1) or as a prefix length (for

example, /24).

Soft Reconfiguration Inbound

Soft reconfiguration enables the router to store all updates from a neighbor in case the inbound policy is

changed. The command is issued in BGP Neighbor Configuration mode and allows a network

administrator to reconfigure BGP policies without clearing active BGP sessions. Administrators can then

institute new policies at any time without forcing the neighbors to reestablish their connection and possibly

disrupt traffic.

BGP updates are stored prior to filtering; thus, allowing the clear ip bgp soft command to be used in the

absence of route refresh (RFC 2918) capability. The unfiltered table is used when an inbound policy is

changed; allowing the router to implement policy changes immediately based on the stored table instead of

having to wait on a new table to be built after a hard reset. A soft reset is beneficial over a hard reset

because it allows policy updates without disrupting network traffic flow. A hard reset terminates the

existing BGP session, effectively removing all routes learned from a neighbor. A new session is then

created and all of the routes must be relearned. Because this process takes place with a hard reset, a

network outage can potentiality occur until the BGP database and route table have been rebuilt.

Use the soft-reconfiguration inbound command to enable the AOS device to store BGP updates for the

specified neighbor:

(config-bgp-neighbor)#soft-reconfiguration inbound

Refer to Example 6 on page 46 for a detailed BGP configuration example where route maps

are applied inbound and outbound to different BGP neighbors.

If no IPv4 address is configured at BGP startup, it uses the highest IPv4 address configured

on a loopback interface. If no loopback interfaces are configured, it uses the highest IPv4

address configured on any interface that is active. If the specified router ID is changed,

existing sessions with BGP neighbors are reset.

Refer to Clear IP BGP on page 74 for more information on this command.