Ospf Overview - Alcatel-Lucent OmniAccess 700 Cli Configuration Manual

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Open Shortest Path First
OSPF O
VERVIEW
OSPF is an IGP (Interior Gateway Protocol) developed by the OSPF working
group of the IETF (Internet Engineering Task Force). RIP (Routing Information
Protocol), an older routing protocol is also used by several corporate networks.
Like RIP, OSPF is designated by the IETF as one of the several IGPs. OSPF is
replacing RIP as the favoured router protocol in larger autonomous system
networks.
OSPF was designed expressly for the IP networks. OSPF supports IP subnetting
and tagging of externally derived routing information. Packet authentication and
sending and receiving packets using IP multicast are also supported in OSPF.
Using OSPF, a host that obtains a change to a routing table or detects a change in
the network immediately multicasts the information to all other hosts in the
network so that all will have the same routing table information. Unlike RIP, in
which the entire routing table is sent, the host using OSPF sends only the part that
has changed. With RIP, the routing table is sent to a neighbor host every 30
seconds. OSPF multicasts the updated information only when a change has taken
place.
Instead of counting the number of hops, OSPF bases its path descriptions on "link
states" that take into account additional network information. OSPF also lets the
user assign cost metrics to a given host router so that some paths are given
preference. OSPF supports a variable network subnet mask so that a network can
be subdivided.
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