Alcatel-Lucent 7450 ESS Series, Руководство по настройке, Страница: 38 / 540

Page 38 7450 ESS OS Router Configuration Guide
Confederations
Configuring confederations is optional and should only be implemented to reduce the IBGP mesh
inside an AS. An AS can be logically divided into smaller groupings called sub-confederations and
then assigned a confederation ID (similar to an autonomous system number). Each sub-
confederation has fully meshed IBGP and connections to other ASs outside of the confederation.
The sub-confederations have EBGP-type peers to other sub-confederations within the
confederation. They exchange routing information as if they were using IBGP. Parameter values
such as next hop, metric, and local preference settings are preserved. The confederation appears
and behaves like a single AS.
Confederations have the following characteristics.
• A large AS can be sub-divided into sub-confederations.
• Routing within each sub-confederation is accomplished via IBGP.
• EBGP is used to communicate between sub-confederations.
• BGP speakers within a sub-confederation must be fully meshed.
• Each sub-confederation (member) of the confederation has a different AS number. The AS
numbers used are typically in the private AS range of 64512 — 65535.
To migrate from a non-confederation configuration to a confederation configuration requires a
major topology change and configuration modifications on each participating router. Setting BGP
policies to select an optimal path through a confederation requires other BGP modifications.