10.9
OSPF
OSPF (Open Shortest Path First) is a routing protocol based on link state and also an internal
gateway protocol, which is developed and recommended by IETF. The OSPF protocol standard
in current use for IPv4 network is OSPF Version 2, which is defined specifically in RFC2328 and
will be introduced generally in this Guide.
Introduction
1.
OSPF Features
OSPF protocol is a popular routing protocol in networking with the following features.
Fast convergence – It could send update packets immediately upon the change of network
topology, to quickly synchronize the update for the routers in the autonomous system.
Due to the rapid convergence, OSPF routing protocol acts with great speediness and
stability in the large-scale network, and is not prone to some harmful routing information.
OSPF protocol introduces the concept of area – to manage the autonomous system by
area, which means the routers only need to synchronize the link state database with the
other routers in the same area. Thus, the smaller link state database requires lower
memory consumption from the routers, and the less routing information to manage also
releases certain CPU resources for the routers and meanwhile reduces the network
bandwidth occupied by the routing information.
OSPF protocol supports multiple equal-cost routes to one destination for load balance,
thus to perform more efficient data forwarding.
OSPF supports VLSM route addressing by variable-length subnet mask.
OSPF supports the message authentication based on interfaces, thus to guarantee the
security of message interaction and routing calculation.
OSPF supports using the reserved multicast address in the link of specific network type, to
reduce the influence on the other irrelevant routers.
2.
OSPF Common Scenario
OSPF protocol is usually applied in the large complex network environment. Shown as below is
the instance diagram of a large company, where the large network is divided by department.
OSPF protocol works as the fundamental routing protocol among routers, which could
guarantee not only the message interaction but also the network independence among
departments.
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