View - ADTRAN Support Community

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
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.
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.
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
61200860L1-29.4E Copyright © 2012 ADTRAN, Inc. 19