BEAME@SSCvax.McMaster.CA (06/14/88)
After reading the documents regarding subnets, I still have one outstanding question with the specifics of BSD/SUN routing from one subnet to another. Is it possible to use the following numbering scheme and provide complete inter-communication: +-------+---------------- Class B Network -----------+--------+ | | +--+--+ +--+--+ | SUN1| | SUN2| +--+--+ +--+--+ | | | +-----+ +-----+ | +--+ SUN3| | SUN4+---+ (Class C Network) | +-----+ +-----+ | | | . (Class C Network) . . . . . Where SUN1 and SUN2 are on the same Class B network (0 subnet bits) and SUN3 and SUN4 use the same Class C number, but with 4 bits used for subnetting. Will SUN1 route packets, from SUN3 destined to SUN4, to SUN2 when the destination is the same Class C number except that the subnet bits are different ? - Carl Beame Beame@McMaster.CA Beame@McMaster.BitNet
jas@proteon.COM (John A. Shriver) (06/14/88)
Subnets of a given subnet must be contiguous. The definition of contiguous is that all subnets of the net are reachable via routes internal to that network. It's in RFC 950 and RFC 1009. The whole point of subnets is to hide the internal structure of a network from all other networks. In your example, the Class C network has been split, and is not contiguous, since traffic between the subnets must cross the Class B network. Since hosts on the Class B network are routing to the Class C network on a network (not subnet) basis, how will they know whether to send traffic for SUN3 via SUN1 or SUN2? Looking at your configuration, subnet your Class B network, using from 4 to 8 subnet bits. Make each Ethernet one subnet. Subnetting Class C networks is not typical. If there are some hosts on the backbone Ethernet that don't know from subnets, you may be able to fake them out using proxy ARP subnet routing. However, they had better age their ARP cache if they do this.