ECMP Configuration

Description

Equal-cost multi-path routing (ECMP) is a routing strategy where you manually define a static route to a number of next-hop gateways. It potentially offers substantial increases in bandwidth by load-balancing traffic over multiple paths to reach the destination network defined in the static route.

Syntax

set static-route <network> nexthop gateway address <gw ip address> on

Example

set static-route 50.50.50.0/24 nexthop gateway address 20.20.20.101 on

set static-route 50.50.50.0/24 nexthop gateway address 20.20.20.102 on

set static-route 50.50.50.0/24 nexthop gateway address 20.20.20.103 on

Notes

To reach addresses on the 50.50.50.0/24 network, packets must first be forwarded to one of these gateways:

• 20.20.20.101
• 20.20.20.102
• 20.20.20.103

To make sure static routes to the next-hop gateways are being enforced, run:

> show route static

1_01:

Codes: C - Connected, S - Static, R - RIP, B - BGP,O - OSPF IntraArea (IA - InterArea, E - External, N - NSSA)A - Aggregate, K - Kernel Remnant, H - Hidden, P - Suppressed

S 0.0.0.0/0  via 192.168.33.1, eth2-01, cost 0, age 2092 

5.5.5.0/24  via 20.20.20.101, eth1-01, cost 0, age 322 

            via 20.20.20.102, eth1-01 

            via 20.20.20.103, eth1-01 

The output shows that the static route to 50.50.50.0/24 is via three next-hop gateways.

Disabling ECMP

ECMP is enabled by default. To disable it:

1. Open this file for editing:

   $PPKDIR/boot/modules/simkern.conf

   If simkern.conf does not exist, create it.

2. Add this line:

   sim_routing_by_source=0

3. Save the file and reboot.