I am studying Networking, and I find

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the Area, Area connect to the Backbone Area is through one path, is it means only through one router(or say not more)?

we often hear that the Internet router are like a net structure, how to explain this?

and why there use and to represent the Area number?


I mean, in general, is the AS Area connect to the Area0 is only through one link?

  • An area can be connected to Area 0 through multiple links. OSPF will then route traffic from the area through the ABR closest to the destination, unless it is a stub area, then it could get routed though any ABR.
    – Ron Maupin
    Oct 11, 2018 at 11:05

1 Answer 1


It is possible that multiple areas are connected to Area 0 (backbone) through different interfaces on a single router, or they may each use a different Area 0 router. To connect two areas through a single link would be something like switched ethernet, where the Area 0 router and the other area routers are connected on a shared medium. There is also the possibility of using a virtual link so that one area connects to Area 0 through another area.

OSPF doesn't really have anything to do with the public Internet, which uses BGP as its routing protocol.

An area number is simply a 32-bit number, as are IP addresses. It is perfectly valid to represent Area 0 as 0 or in dotted-decimal notation as, like an IP address. Just do not confuse the area number, or an OSPF router ID (also a 32-bit number that can be represented in dotted-decimal notation), with an actual IP address.

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