IP Routing Features

Configuring OSPF

When multiple Series 5300XL Switches on the same network are declaring themselves as DRs, then both priority and router ID are used to select the designated router and backup designated routers.

When only one router on the network claims the DR role despite neighboring routers with higher priorities or router IDs, this router remains the DR. This is also true for BDRs.

The DR and BDR election process is performed when one of the following events occurs:

an interface is in a waiting state and the wait time expires

an interface is in a waiting state and a hello packet is received that addresses the BDR

a change in the neighbor state occurs, such as:

 

• a neighbor state transitions from 2 or higher

 

• communication to a neighbor is lost

 

• a neighbor declares itself to be the DR or BDR for the first time

 

OSPF RFC 1583 and 2328 Compliance

 

HP Series 5300XL Switches are configured, by default, to be compliant with

 

the RFC 1583 OSPF V2 specification. HP Series 5300XL Switches can also be

 

configured to operate with the latest OSPF standard, RFC 2328.

 

 

N o t e

For details on how to configure the system to operate with the RFC 2328, see

 

“Configuring OSPF” on page 16-37.

 

Reduction of Equivalent AS External LSAs

 

 

An OSPF ASBR uses AS External link advertisements (AS External LSAs) to

 

originate advertisements of a route to another routing domain, such as a RIP

 

domain. The ASBR advertises the route to the external domain by flooding AS

 

External LSAs to all the other OSPF routers (except those inside stub

 

networks) within the local OSPF Autonomous System (AS).

 

In some cases, multiple ASBRs in an AS can originate equivalent LSAs. The

 

LSAs are equivalent when they have the same cost, the same next hop, and

 

the same destination. The HP switch optimizes OSPF by eliminating duplicate

 

AS External LSAs in this case. The switch with the lower router ID flushes the

 

duplicate External LSAs from its database and thus does not flood the dupli­

 

cate External LSAs into the OSPF AS. AS External LSA reduction therefore

 

reduces the size of the switch’s link state database.

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