stanonik@NPRDC.ARPA.UUCP (06/12/86)
Now that subnetting (and subnet arp support) is available, some questions arise about using it, particularly about making the transition to subnets. The local network (class B) currently consists of a main cable to which every host is directly attached. Because subnetting was anticipated, addresses were assigned in a subnet fashion; ie, the third byte (intended to become the subnet number) grouped machines. That however seems to cause a problem for the transition to subnets. To any subnet branching off the main cable, the addresses of those not yet capable of subnetting make the main cable look like a collection of subnets. Yuck! 4.3bsd doesn't seem to allow more than one subnet per interface (cable), so many of those hosts will be unreachable. A nice(?) solution would be to continue to treat the main cable as unsubnetted (netmask 0xffff0000) and only route to it packets not bound for known subnets, but 4.3bsd doesn't seem to do this. Have we overlooked some routing trick, or must everyone remaining on the main cable change addresses to one subnet number? Thanks, Ron Stanonik stanonik@nprdc.arpa
JNC@XX.LCS.MIT.EDU ("J. Noel Chiappa") (06/12/86)
I don't think there's any easy way to do this if you can't make your 4.3 gateway accept more than one IP address for a single interface. I guess you've considered the obvious brute-force solutions like putting N different interfaces in your gateway machine, or getting another class B network and making that the subnetted net. Being able to assign a single physical net several logical net numbers makes renumbering things really painless; you don't have to have a massive flag day. That's such a useful capability for a gateway to have that I'm surprised 4.3 is missing it; are you sure there's no way to do it? Maybe someone should or has added it to 4.3. Of course, the difficulty factor of doing this will really depend on how the insides of the 4.3 IP layer are arranged. I can tell you from experience in the C Gateway that some places you really have to work at it to make things work with multiple addresses per interface. Consider sending out routing packets (you can't use the all 1's broadcast address since people may get routing packets intended for the other logical net), checking for incoming broadcast packets, etc! Noel -------