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