![]() In the United States, many of these backbones are run by telecommunication companies such as AT&T, Bell South, Congent, Qwest, Level 3, MCI/Worldcom, Sprint, and Time Warner. The first Internet backbone was between UCLA and SLI on October 29, 1969, and today the Internet consists of several large backbones that carry the majority of traffic throughout the world. The backbone often connects large networks or companies together. If this requirement is not met, all traffic destined for the areas not connected to such an ABR or out of the OSPF domain, is dropped.A portion of a computer network that is capable of carrying the majority of traffic on the network at high speeds. "Though the definition of the Area Border Router (ABR) in the OSPF specification does not require a router with multiple attached areas to have a backbone connection, it is actually necessary to provide successful routing to the inter-area and external destinations. Just my two cents )įound this in the abstract of RFC 3509 (Alternative Implementations of OSPF ABRs): However, the main functionaltity I associate with an ABR is inter-area routing, and this doesn't happen (at least not for their neighbor-routers) without a backbone connection. Hard to say what John Moy had in mind when he choosed such formulations. Instead you can find statements like this:ģ.1 (.) "The OSPF backbone always contains all area border routers." It wasn't my intention to say Rick's answer is incorrect, and I understand Rick's and your point: The RFC indeed doesn't say explicitly that an OSPF router is not an ABR when it doesn't have a backbone connection. By the RFC, though, that appears to be incorrect, although again, that's normal usage.) (BTW, without reading the RFC information posted by Rolf, off-the-cuff, I would have answered OP question that an ABR requires an area zero connection in addition to another area or areas connections. ABRs are usually also, by RFC definition, "backbone" routers too. Having an ABR w/o an area zero connection would be unusual. However, it won't share one area's routing information with another area's OSPF neighbors w/o area zero. ![]() An area zero connection isn't required.Īn OSPF router configured as an ABR, without a connection to area zero, will route traffic within and even between its connected areas. an ABR is just an OSPF router connected to more than one area. Hmm, I would say Rick's answer, from the RFC, is correct, i.e. In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage. Usage of this posting's information is solely at reader's own risk. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Routers with all interfaces connecting to the backbone area are supported.Īs you know, that's sometimes the trouble especially with the larger RFCs: The information is often divided over several paragraphs and even chapters. However, backbone routers do not have to be area border routers. This includes all routers that interface to more than one area (i.e., area border routers). The backbone in turn distributes the information to the other areas.Ī router that has an interface to the backbone area. I agree that the "Area border router" paragraph of RFC 2328 doesn't state the backbone area requrirement but the very next ("Backbone routers") does:Ī router that attaches to multiple areas.Īrea border routers run multiple copies of the basic algorithm, one copy for each attached area.Īrea border routers condense the topological information of their attached areas for distribution to the backbone. ![]() A strict reading of the RFCs about OSPF basically says that ABR connects two areas and does not specifically require that one be area 0.
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