oreilly@netcom.ubc.ca (Dennis O'Reilly) (11/02/90)
We have a serious problem here at the University of British Columbia. The problem is our Ethernet attached Mac's that use MacTCP 1.0.1 do not work on our network. The problem is as follows: (a) A Mac is on an Ethernet segment that is controlled by a IP router. (b) There are 3 IP subnets on this Ethernet segment. 137.82.27.x, 137.82.28.x, and 137.82.29.x (c) RIP packets are broadcast on each of these subnets to the subnet only. That is, the RIP packets for subnet 137.82.27.x have a destination IP adddress of 137.82.27.255 (d) Each RIP packet advertises a default gateway for its subnet (e) The Mac is on the 137.82.28.x subnet. It's IP address (as assigned through the MacTCP control panel) is 137.82.28.47). The gateway address is 137.82.28.254. The subnet mask is 255.255.255.0. (d) When I restart the Mac and run a TCP/IP application, it works for a few seconds, until I receive a RIP packet for one of the other subnets. (e) Then the Mac just freezes dead (f) If you look at an Ethernet trace when the Mac is frozen you can see it is ARPing to find the transceiver address for a default gateway on a different subnet than the one it is on. (g) Of course, the IP router never responds to the ARP. It would be incorrect for it to do so since one subnet should not be visible to another subnet. (h) My suspicion is that MacTCP hears RIP packets on subnets other than its own and errantly changes its default gateway. I guess it's listening to RIP packets for the whole network rather than for just the subnet its on. It's legitimate to listen for RIP packets for the whole network but only if they are broadcast to the network (that is, sent to 137.82.255.255 and not 137.82.28.x). In summary, it appears that MacTCP 1.0.1 does not work if you have more than one subnet on the same Ethernet segment. If anyone knows of a way around this problem I'd appreciate hearing about it. Maybe there is a later release of MacTCP that I haven't heard about?? Thanks. Dennis O'Reilly Internet: oreilly@netcom.ubc.ca Networking & Communications Bitnet: oreilly@ubcmtsg University of B.C. Phone: (604) 228-3072 Vancouver, Canada V6W 1T5 Fax: (604) 228-5520