Technical data

BLADE OS 5.1 Application Guide
BMD00136, November 2009 Chapter 8: Basic IP Routing
 121
ECMP Static Routes
Equal-Cost Multi-Path (ECMP) is a forwarding mechanism that routes packets along multiple paths
of equal cost. ECMP provides equally-distributed link load sharing across the paths. The hashing
algorithm used is based on the source IP address (SIP). ECMP routes allow the switch to choose
between several next hops toward a given destination. The switch performs periodic health checks
(ping) on each ECMP gateway. If a gateway fails, it is removed from the routing table, and an
SNMP trap is sent.
OSPF Integration
When a dynamic route is added through Open Shortest Path First (OSPF), the switch checks the
route’s gateway against the ECMP static routes. If the gateway matches one of the single or ECMP
static route destinations, then the OSPF route is added to the list of ECMP static routes. Traffic is
load-balanced across all of the available gateways. When the OSPF dynamic route times out, it is
deleted from the list of ECMP static routes.
For more information about OSPF, refer to “OSPF” on page 145.
ECMP Route Hashing
You can configure the parameters used to perform ECMP route hashing, as follows:
 sip: Source IP address (default)
 dipsip: Source IP address and destination IP address
The ECMP hash setting applies to all ECMP routes.
Configuring ECMP Static Routes
To configure ECMP static routes, add the same route multiple times, each with the same destination
IP address, but with a different gateway IP address. These routes become ECMP routes.
1. Add a static route (IP address, subnet mask, gateway, and interface number).
2. Add another static route with the same IP address and mask, but a different gateway address.
3. Select an ECMP hashing method (optional).
RS G8000 (config)# ip route 10.10.1.1 255.255.255.255 100.10.1.1 1
RS G8000 (config)# ip route 10.10.1.1 255.255.255.255 200.20.2.2 1
RS G8000 (config)# ip route ecmphash {sip|dipsip}