
Configuring IP Services
1-10
Open Shortest Path First (OSPF) Protocol
The Open Shortest Path First (OSPF) protocol is an 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.
For a more detailed overview and OSPF configuration information, see Chapter 4.
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.
For a more detailed overview and BGP configuration information, see Chapter 5.
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