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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.
Not 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.
16-35