whna@cgch.UUCP (Heinz Naef) (09/11/89)
Hello Neighbors, the article on OSPF in ConneXions Aug. 89 says: "... An area is a generalization of a subnetted network; it should be noted that all subnets of a network must be contained within a single area." Assume a large organization having a single Class B Network Number divided into subnets. The subnet number space is partitioned into groups to form clusters of a certain amount of autonomy. It would be highly desirable to treat each of these groups as an OSPF routing area in order to establish a hierarchical routing scheme, combined with routing firewalls for enhanced overall availability, reliability and security. Is our interpretation correct that OSPF, instead of allowing to break down a subnetted network into areas, is based on a model which groups subnetted networks together within one area? If yes, then this is a new form of the Autonomous System concept, isn't? What's the difference? Any suggestions what could be done to implement *our* model? Remember, the network described above is *not* connected to The Internet. Could anyone who is actively dealing with OSPF send a short message back including references to further information available about OSPF? We are very interested in this development and would like to discuss further aspects. Thanks in advance, and best regards, Heinz Naef, c/o CIBA-GEIGY AG, R-1045.3.37, P.O.Box, CH-4002 Basel, Switzerland UUCP: cgch!whna Internet: whna%cgch.uucp@uunet.uu.net Phone: (+41) 61 697 26 75 BITNET: whna%cgch.uucp@cernvax.bitnet Fax: (+41) 61 697 32 88
medin@NSIPO.NASA.GOV ("Milo S. Medin", NASA ARC NSI Project Office) (09/12/89)
Not true. In an older draft of the spec, that was the case. In the current spec (which has just been submitted for publication as an RFC - should be out soon), the area boundaries can occur on internal subnet boundaries. That is, you could collapse the area routing information on subnet boundaries (with a given mask) and not to the natural mask of the network. The packet formats were changed so that this could occur. Van Jacobson at LBL and John Larson (who used to be at Xerox PARC) all had very good reasons for why the spec should be this way. The reason it wasn't that way in the first place was an attempt to try and simplify the protocol, but upon careful examination, it didn't really simplify much (except configuration) since you already had to deal with variable length subnet mask support. If you think it was bad for you, think of a large company who uses a single Class A network number for their internal system. Running such a system as a single area would have defeated the whole reason areas were introduced in the specification. In addition, since the authentication type is configurable on a per area basis, areas can be fairly autonomous. Since OSPF areas also act as routing firewalls (an intra-area path is NEVER overriden by an inter-area path), there are reasons why one would use areas in cases where the topological complexity wouldn't justify it alone. Also note, that it's VERY hard to do this unless you have variable length subnet mask support. Since OSPF handles this, it's not a problem, but this issue can a very sticky one to deal with. Thanks, Milo
jmoy@proteon.com (John Moy) (09/12/89)
Heinz- OSPF is an Internal Gateway Protocol, which means that it is a routing protocol that runs internal to a single Autonomous System. OSPF further lets you break the Autonomous System into areas. OSPF areas provide a means for hiding, condensing and protecting routing information. OSPF areas are defined to be lists of IP address ranges. This means that several subnetted networks can be contained within a single OSPF area; for example, if the two class B networks 128.185.0.0 and 128.186.0.0 are subnetted, an OSPF area could be defined as: OSPF area 1: 128.185.0.0 - 128.185.255.255 and 128.186.0.0 - 128.186.255.255 Alternatively, a single subnetted network can be broken up into multiple OSPF areas. This is what I think you would want to do. For example, the above subnetted network 128.185.0.0 could be split into the OSPF areas: OSPF area 1: 128.185.0.0 - 182.185.15.255 OSPF area 2: 128.185.16.0 - 128.185.31.255 ... OSPF area 16: 128.185.240.0 - 128.185.255.255 The OSPF specification is available for anonymous ftp from the Internet Engineering Task Force's Internet-Draft directory on NIC.DDN.MIL. It's in postscript format, file name DRAFT-IETF-OSPFIGP-SPEC-07.PS. John