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Router Node 21
information for the autonomous system. Here is the list of interior
protocols supported by the GRF:
• RIP
The Routing Information Protocol (RIP), as delivered with most UNIX
systems, is run by the routing deamon
routed
. During the startup of
routed
a request for routing updates is issued. After that, the daemon
listens for responses to the request. Systems that are configured to
supply RIP information hear this request and respond with update
packets based on the information in the system’s routing table. The
update packets contain the destination addresses from the routing
table and the routing metrics associated with each destination. Update
packets are send on request and periodically to keep routing
information accurate.
•OSPF
Open Shortest Path First
(OSPF) is defined by
RFC
2178 (Request for
Comments). It is a link-state protocol and very different from RIP. A
router running RIP shares information about the entire network with its
neighbors. A router running OSPF shares information about its
neighbors with the entire network. The "entire network" means, at
most, a single autonomous system. OSPF further defines a hierarchy
of routing areas within an autonomous system:
• Areas
These are sets of networks within a single autonomous system that
have been grouped together. The topology of an area is hidden from
the rest of the autonomous system, and each area has a separate
topology database. Routing within the autonomous system takes
place on two levels, depending on whether the source and
destination of a packet reside in the same area (
intra-area routing
)
or different areas (
inter-area routing
).
Intra-area routing is determined only by an area’s own topology.
That is, the packet is routed solely on information obtained within
the area.
Inter-area routing is always done via a
backbone
.
The dividing of an autonomous system into areas enables a
significant reduction in the volume of routing traffic required to
manage the routing database for a large autonomous system.
• Backbone
The backbone consists of those networks not contained in any area,
their attached routers, and routers that belong to multiple areas.