Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 54)

26 Multi-Service IronWare Routing Configuration Guide
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Enabling or disabling comparison of device IDs
NOTE
If the cluster contains more than one route reflector, you need to configure the same cluster ID on
all the route reflectors in the cluster. The cluster ID helps route reflectors avoid loops within the
cluster.
Enabling or disabling comparison of device IDs
Device ID comparison is Step 11 in the algorithm BGP4 uses to select the next path for a route.
NOTE
Comparison of device IDs is applicable only when BGP4 load sharing is disabled.
When device ID comparison is enabled, the path comparison algorithm compares the device IDs of
the neighbors that sent the otherwise equal paths:
• If BGP4 load sharing is disabled (maximum-paths 1), the device selects the path that came
from the neighbor with the lower device ID.
• If BGP4 load sharing is enabled, the device load shares among the remaining paths. In this
case, the device ID is not used to select a path.
NOTE
Device ID comparison is disabled by default.
To enable device ID comparison, enter the compare-routerid command at the BGP4 configuration
level of the CLI.
Brocade(config-bgp)# compare-routerid
Syntax: [no] compare-routerid
For more information, refer to “How BGP4 selects a path for a route (BGP best path selection
algorithm)” on page 5.
Configuring confederations
A confederation is a BGP4 Autonomous System (AS) that has been subdivided into multiple,
smaller ASs. Subdividing an AS into smaller ASs simplifies administration and reduces
BGP4-related traffic, which in turn reduces the complexity of the Interior Border Gateway Protocol
(IBGP) mesh among the BGP4 devices in the AS.
The implementation of this feature is based on RFC 3065.
Normally, all BGP4 devices within an AS must be fully meshed, so that each BGP4 device has BGP4
sessions to all the other BGP4 devices within the AS. This is feasible in smaller ASs, but becomes
unmanageable in ASs containing many BGP4 devices.
When you configure BGP4 devices into a confederation, all the devices within a sub-AS (a
subdivision of the AS) use IBGP and must be fully meshed. However, devices use EBGP to
communicate between different sub-ASs.
Another way to reduce the complexity of an IBGP mesh is to use route reflection. However, if you
want to run different Interior Gateway Protocols (IGPs) within an AS, you must configure a
confederation. You can run a separate IGP within each sub-AS.