Configuring Ospf - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

Using the Web Browser Interface for Advanced Configuration Tasks
Routing
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Configuring OSPF

OSPF is a link-state routing protocol. Rather than advertising actual routes,
routers advertise links—connections to other routers and connections to
networks. A router uses the link-state advertisements (LSAs) that it receives
to compile an OSPF database. This database is exactly the same as the
database of every other router in the OSPF network. (When routers have
established that they are using the same database, they have achieved adja-
cency.) From this shared database, each router computes its own best routes
to every destination in the network.
When a router advertises a link, it also advertises a cost for that link. Routers
compute the best route to a destination by summing the cost of every link en
route to that destination and choosing the route with the lowest cost. Unlike
RIP, therefore, OSPF can choose routes according to other factors besides
hop-count. Generally, a link's cost is inversely proportional to its bandwidth.
Because a WAN may have connections with greatly varying bandwidth, OSPF
is well-suited to a WAN environment.
In a large network, a router may receive many LSAs, and its OSPF database
may become quite large. You can divide your network into areas to minimize
the strain OSPF places on bandwidth and router processes.
Areas divide a network into routing domains. A router in one area only has to
only maintain the same database as other routers in that area. A network
backbone, or area 0, connects all areas. Area 0 includes area border routers
(ABRs), which have interfaces in, and store routing information for, multiple
areas. ABRs advertise summary LSAs to routers in non-backbone areas so that
these routers can route traffic to destinations in areas beyond their own.
OSPF defines several different types of areas. Stub areas are areas that do not
transit traffic. Routers in stub areas do not receive LSAs for external traffic,
which in some networks can dramatically decrease the number of LSAs
routers must process. Instead stub routers receive a default route for external
traffic from their ABR.
The ProCurve Secure Router supports the configuration of stub areas. How-
ever, you cannot configure stub areas from the Web interface. If other routers
in your network define an area in which your router resides as a stub area,
your router will not be able to achieve adjacency with them. You must access
the CLI and configure the stub area. (See Chapter 13: IP Routing—Configur-
ing RIP, OSPF, BGP, and PBR for instructions on how to do so.)