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Dynamic Routing
OSPF
Open Shortest Path First ( OSPF ) is a most widely used interior gateway protocil (IGP) for Internet
Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing
protocols, operating within a single autonomous system (AS).
OSPF allows collections of rotuers to be grouped together. Such a group is called an area (AS). Each
area runs a seprate copy of the basic link-state routing algorithm. This means that each area has its
own link-state database and cooresponding shortest path tree.
The structure of an area is invisible from other areas. This isolation of knowledge makes the protocol
more scalable if multiple areas are used.
The most widely used exterior gateway protocol is the Border Gatewat Protocol (BGP), which will be
our next topic, the pricipal routing protocol between autonomous systems on the itnernet.
OSPF: Enable to actiavte OSPF routing.
Rule Index: A totoal 10 OSPF rules are allowed, ranging from 0 to 9.
Interface: Set the interface which runs the OSPF process (involved in OSPF routing). It can be WAN
interfaces or established GRE tunnels.
Area ID: The OSPF area identifier. It is a decimal number in the rang of 0-4294967295. Here to set the
area ID which the inteface belongs to. The area with area-id=
”0” is the backbone area.
If the router has networks in more than one area, then an area with area-id=
”0” (the backbone) must
always be present. All other areas are connected to it. The backbone is responsible for distributing
routing information between non-backbone areas. The backbone must be contiguous, i.e. there must
be no disconnected segments. However, area border routers do not need to be physically connected
to the backbone - connection to it may be simulated using a virtual link.