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BLADEOS 6.5.2 Application Guide
BMD00220, October 2010 Chapter 20: OSPF 287
Host Routes for Load Balancing
BLADEOS implementation of OSPF includes host routes. Host routes are used for advertising
network device IP addresses to external networks, accomplishing the following goals:
ABR Load Sharing
As a form of load balancing, host routes can be used for dividing OSPF traffic among multiple
ABRs. To accomplish this, each switch provides identical services but advertises a host route
for a different IP address to the external network. If each IP address serves a different and equal
portion of the external world, incoming traffic from the upstream router should be split evenly
among ABRs.
ABR Failover
Complementing ABR load sharing, identical host routes can be configured on each ABR.
These host routes can be given different costs so that a different ABR is selected as the
preferred route for each server and the others are available as backups for failover purposes.
Equal Cost Multipath (ECMP)
With equal cost multipath, a router potentially has several available next hops towards any
given destination. ECMP allows separate routes to be calculated for each IP Type of Service.
All paths of equal cost to a given destination are calculated, and the next hops for all equal-cost
paths are inserted into the routing table.
If redundant routes via multiple routing processes (such as OSPF, RIP, BGP, or static routes) exist
on your network, the switch defaults to the OSPF-derived route.
OSPF Features Not Supported in This Release
The following OSPF features are not supported in this release:
Summarizing external routes
Filtering OSPF routes
Using OSPF to forward multicast routes
Configuring OSPF on non-broadcast multi-access networks (such as frame relay, X.25, or ATM)