Routing With Ospf - HP 200 Series Services And Applications

Routing with OSPF

The capabilities of an internet are largely determined by its routing protocol.
An internet's scalability, its ability to quickly route around failures, and the
consumption of network resources by the routing machinery are all issues
directly related to the routing protocol. With the release of HP router soft-
ware revision 5.70, OSPF (Open Shortest Path First) is available in addition
to RIP.
RIP (Routing Information Protocol) is probably the most widely used IP
routing protocol. Its popularity stems from having been included with
Berkeley UNIX (Routed, the routing daemon) and from being standardized
by the IETF (Internet Engineering Task Force). RIP is documented in RFC
(Request for Comments) 1058. RIP is a distance-vector protocol. A distance-
vector protocol frequently (at 30-second intervals for RIP) sends its routing
table (a vector of distances) to neighbor (adjacent) routers. When a router
receives its neighbor's routing update, it compares the update with its own
routing table and changes its routing table if necessary.
Distance-vector protocols are susceptible to two main problems. First, they
can form routing loops, and second, they can be slow to converge. Conver-
gence is the time required for the routing tables in all of the connected
routers to stabilize after an event such as a network link failure. Routing
loops and slow convergence are more likely to occur as network size and
complexity increase. A fundamental assumption for routing (in the design of
RIP) was that the internet contained at most a few hundred networks. Thus,
RIP is not well suited for use with today's large corporate and government
internets, which have thousands of networks. The limitations inherent in
distance-vector protocols such as RIP and the lack of a standard routing
protocol suitable for use in large internets are in large part responsible for
the development of OSPF.
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