
Configuring IP Services
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Open Shortest Path First (OSPF) Protocol
The Open Shortest Path First (OSPF) protocol is an interior gateway protocol
(IGP) intended for use in large networks. Using a link state algorithm, OSPF
exchanges routing information between routers in an autonomous system. Routers
synchronize their topological databases. Once the routers are synchronized and
the routing tables are built, the routers will flood topology information only in
response to some topological change. For OSPF, the “best” path to a destination is
the path that offers the least cost metric delay. In OSPF, cost metrics are
configurable, allowing you to specify preferred paths.
OSPF supports CIDR and can carry supernet advertisements within a routing
domain.
Border Gateway Protocol (BGP)
The Border Gateway Protocol (BGP) is an exterior gateway protocol used to
exchange network reachability information with other BGP systems. BGP routers
form relationships with other BGP routers. Using an entity called a BGP speaker,
BGP routers transmit and receive current routing information over a reliable
transport layer connection. Because a reliable transport mechanism is used,
periodic updates are not necessary.
BGP updates contain “path attributes” that describe the route to a set of
destination networks. When multiple paths are available, BGP compares these
path attributes to choose the preferred path.
BGP-3 and BGP-4 are supported. BGP-4 is the border gateway protocol that
supports CIDR.
Exterior Gateway Protocol (EGP)
The Exterior Gateway Protocol (EGP-2) is an exterior gateway protocol used to
exchange network reachability information between routers in different
autonomous systems. An IGP, such as RIP or OSPF, is used within an AS to
facilitate the communication of routing information within the autonomous
system. The routers that serve as the end points of a connection between two
autonomous systems run an exterior gateway protocol, such as EGP-2.
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