Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 711)

Route Selection
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 28.7
Metric
The Metric is used to find the best route from one routing source. In the routing table it is
used as the next tie breaker if the Administrative Distance (AD) is equal for the routes in it.
Metrics Used by AlliedWare Plus Routing Protocols
The following metrics are used by AlliedWare IPv4 and IPv6 routing protocols:
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
Operating System 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
Operating System 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:
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.
How AlliedWare Plus Deletes Routes
When the AlliedWare Plus
TM
Operating System receives a route delete request from a
routing protocol, it first deletes the specified route from its RIB. Then it checks if the
specified route is in the FIB.
If the route is in the FIB, it deletes it from the FIB and checks if another route is available in
its database for the same prefix.
If there is another route in the database, the software installs this route in the FIB. When
multiple such routes exist, the software uses the route selection mechanism to choose the
best route before adding it to the FIB.
IPv4 and IPv6 Routing Protocol Metric
RIP for IPv4 / RIPng for IPv6 Hop-Count
OSPFv2 for IPv4 / OSPFv3 for IPv6 Cost
BGP for IPv4 / BGP4+ for IPv6 MULTI_EXIT-DISC / IGMP metric to Next-Hop
awplus(config)# maximum-paths <1-8>