Equal Cost Multi Path (Ecmp); Figure 3: Equal Cost Multi Path (Ecmp) - Avaya 8600 Engineering

config vlan 2 ip create 172.3.1.1/24
config vlan 2 ip ospf interface-type
passive
config vlan 2 ip ospf enable

5. Equal Cost Multi Path (ECMP)

ECMP is a feature, which will load balance routed IP traffic across up to four equal cost paths. The
Ethernet Routing Switch 8600 supports ECMP operation for OSPF, RIP, static routes, and default routes.
There are a few benefits of ECMP when used with OSPF:
1) no need to rerun Dijkstra should the main path fail, the other ECMP path(s) will automatically take
the load.
2) loadsharing implies better use of network facilities.
The traffic distribution algorithm is identical to the Multi-Link Trunk (MLT) algorithm for IP datagrams:

MOD (DestIP(X)[5:0] XOR SrcIP(Y)[5:0],#of active links) 'XOR the last 6 bits of the source and
destination IP address, divide by the number of links, and take the remainder.Configuration
Example – ECMP
Configuration of ECMP is quite simple. For example, in reference to PP8600A, the commands to enable
ECMP over two paths is as follows:
config ip ecmp enable
config ip ecmp-max-path 2
After ECMP is configured, ECMP paths can be verified in the routing table. Those paths with an E in the
Type column are designated equal cost paths. In this example we see two routes to 1.1.1.2, and two
routes to 10.1.30.0.
show ip route info
November 2010

Figure 3: Equal Cost Multi Path (ECMP)

ERS 8600 / 8800 OSPF Technical Configuration Guide
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