Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!ub!csn!boulder!recnews From: Watt-Alan@mickey.ycc.yale.edu Newsgroups: comp.dcom.sys.cisco Subject: Re: backplane backbone, routing or bridging? Message-ID: <9106220236.AA11113@mickey.ycc.yale.edu> Date: 22 Jun 91 02:36:13 GMT Sender: news@colorado.edu Organization: University of Colorado, Boulder Lines: 49 Return-Path: Steve Hubert replied to my posting of 20-Jun-91: |On Thu, 20 Jun 91 22:11:40 EDT, Watt-Alan@mickey.ycc.yale.edu wrote: | |> Subject: Re: backplane backbone, routing or bridging? |> To: hubert@cac.washington.edu |> cc: cisco@spot.colorado.edu |> |> ... |> | |> However you do not have to assign a whole subnet to each point-to-point |> ethernet. You can have a single subnet which is shared by all the |> point-to-point ethernets on both ends. Assuming you subnet a class B |> on an 8-bit boundary, and the "point-to-point cloud" is subnet 100, |> you could define the subnet mask 255.255.255.252 to allow 6 bits |> of "sub-subnet" and 2 bits of "host" (0 is reserved, 3 is broadcast, |> 1 and 2 are the two endpoints. | |I don't understand how to do this with cisco equipment. My understanding is |that the cisco has a single netmask for a network. How do you get the |variable length mask idea to work? I think my fingers ran amok before my mind was properly engaged. I have actually never tried this and now that I think about it, it is quite likely to get you in trouble. However, I am quite sure that nothing stops you from getting yourself a new class C network and subnetting it as described above. This still saves you from wasting unnecessary subnets of your class B. For all that, it may actually work to sub-subnet your class B. On a typical BSD system, datagrams would be output on the proper interface, but the routing protocol daemons might get hopelessly confused. Perhaps the same thing would happen on a cisco box (or is it "Cisco box" these days?). - Alan S. Watt High Speed Networking, Yale University Computing and Information Systems Box 2112 Yale Station New Haven, CT 06520-2112 (203) 432-6600 X394 Watt-Alan@Yale.Edu Moral: Think twice, hit once. Disclaimer: It is a violation of federal law to use this posting in a manner inconsistent with this disclaimer.