Nortel Web OS 10.0, Application Manual

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Web OS 10.0 Application Guide
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Chapter 4: OSPF
212777-A, February 2002
Host Routes for Load Balancing
Web OS 10.0 implementation of OSPF includes host routes. Host routes are used for advertis-
ing network device IP addresses to external networks, accomplishing the following goals:
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Server Load Balancing (SLB) within OSPF
Host routes advertise virtual server IP addresses to external networks. This allows stan-
dard SLB between the Web switch and the server pools in an OSPF environment. For
more information on SLB, see
Chapter 6, “Server Load Balancing and your Web OS 10.0
Command Reference.
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ABR Load Sharing
As a second form of load balancing, host routes can be used for dividing OSPF traffic
among multiple ABRs. To accomplish this, each Web switch provides identical services
but advertises a host route for a different virtual server IP address to the external network.
If each virtual server IP address serves a different and equal portion of the external world,
incoming traffic from the upstream router should be split evenly among ABRs.
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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 virtual server and the others are available as backups for failover
purposes.
If redundant routes via multiple routing processes (such as OSPF, RIP, BGP, or static routes)
exist on your network, the Web switch defaults to the OSPF-derived route.
For a configuration example, see “Example 4: Host Routes” on page 92 .
OSPF Features Not Supported in This Release
The following OSPF features are not supported in this release:
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Redistributing routes into OSPF (Web OS 10.0 does not allow your switch to emulate an
ASBR)
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Summarizing external routes
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Filtering OSPF routes
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Configuring equal cost route load balancing
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Using OSPF to forward multicast routes
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Configuring OSPF on non-broadcast multi-access networks (such as frame relay, X.25,
and ATM)