Troubleshooting guide

Additional BGP Configuration

Log Neighbor Changes

Use the bgp log-neighbor-changes command to control the logging of neighbor state changes. This

command controls logging of BGP neighbor state changes (up/down) and resets. This information is useful

for troubleshooting and determining network stability.

(config-bgp)#bgp log-neighbor-changes

Maximum Paths

Use the maximum-paths command to specify the number of equal cost parallel routes (shared paths)

learned by BGP that can be exported to the route table. When IP load sharing is enabled, traffic is balanced

to a specific destination across up to six equal paths.

(config-bgp)#maximum-paths <value>

<value> Specifies the number of equal cost parallel routes learned by BGP that can be exported to the

route table. Valid range is 1 to 6.

Multi-Exit Discriminators (MEDs)

Use the bgp command to instruct AOS on how to handle multi-exit discriminators (MEDs) for all routes

from the same AS.

(config-bgp)#bgp [always-compare-med | compare-med | deterministic-med | ignore-med]

always-compare-med Always compares MEDs for all paths for a route, regardless of the AS through

which the route passes.

compare-med Compares MEDs for all received routes.

deterministic-med Compares the MEDs for all routes received from different neighbors within the same

AS.

ignore-med Disregards MEDs for all received routes.

Next-Hop Self

Use the next-hop-self command to force the NEXT_HOP attribute to be changed to this unit’s IPv4

address for each network it advertises to the neighbor address.

(config-bgp-neighbor)#next-hop-self

IGPs, such as RIP and OSPF, always use the source IPv4 address of a routing update as the next-hop

address for each network that is placed in the routing table. Conversely, since BGP routes AS-to-AS, the

default next hop that is advertised is the next AS. This behavior can present a problem in situations where

an iBGP router learns about networks outside of its AS through one of its iBGP peers. By default, the

next-hop address for the external networks advertised to the iBGP router is the entry point for the next AS.

When the iBGP router receives packets destined for one of the external networks, it performs a recursive

lookup of the entries in its own IGP routing table to determine how to reach the BGP next-hop address.

Unless the iBGP router has a static route or an entry in its IGP routing table indicating how to reach the

edge router in

Refer to Setting a MED Metric on page 28 for information on how to configure the value of

the MED metric advertised outbound to BGP neighbors.