Route Selection
©2008 Allied Telesis Inc. All rights reserved.
25.6
AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E
Software Version 5.2.1
Equal Cost Multipath Routing
When multiple routes are available for the same prefix within the FIB, then your device uses
Equal Cost Multipath Routing (ECMP) to determine how to forward packets.
ECMP allows the AlliedWare Plus
TM
OS to distribute traffic over multiple equal-cost routes to
a destination. The software determines that two or more routes are equal cost if they have the
same destination IP address and mask. When the software learns such multiple routes, it puts
them in an ECMP route group. When it sends traffic to that destination, it distributes the traffic
across all routes in the group.
The AlliedWare Plus
TM
OS distributes traffic over the routes one flow at a time, so all packets
in a session take the same route. Each equal-cost route group can contain up to eight individual
routes. ECMP is only used to select between routes already in the FIB.
By default, each equal-cost route group can contain four routes. You can change this setting by
using the command:
awplus(config)#
maximum-paths <1-8>
The maximum path setting determines how many routes with the same prefix value and the
same administrative distance that the FIB can contain. Once an equal-cost route group has the
maximum number of routes, then the RIB cannot add any further routes to the route group.
The device only adds to the group if a route is deleted from the FIB.
To disable ECMP, set the maximum paths value to one.