HP 3500YL - Manual (Page 224)

IP Routing Features
Configuring OSPF
N o t e s By default, the router ID is typically the lowest-numbered IP address or the
lowest-numbered (user-configured) loopback interface configured on the
device. For more information or to change the router ID, see “Changing the
Router ID” on page 5-15.
If multiple networks exist in the same OSPF area, the recommended approach
is to ensure that each network uses a different router as its DR. Otherwise, if
a router is a DR for more than one network, latency in the router could increase
due to the increased traffic load resulting from multiple DR assignments.
When only one router on an OSPF 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 Area Types
OSPF is built upon a hierarchy of network areas. All areas for a given OSPF
domain reside in the same Autonomous System (AS). An AS is defined as a
number of contiguous networks, all of which share the same interior gateway
routing protocol.
An AS can be divided into multiple areas. Each area represents a collection of
contiguous networks and hosts, and the topology of a given area is not known
by the internal routers in any other area. Areas define the boundaries to which
types 1 and 2 LSAs are broadcast, which limits the amount of LSA flooding
that occurs within the AS and also helps to control the size of the link-state
databases (LSDBs) maintained in OSPF routers. An area is represented in
OSPF by either an IP address or a number. Area types include:
■ backbone ■ not-so-stubby (NSSA)
■ normal ■ stub
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