Thanks to everyone who offered suggestions. In fact everyone said pretty
much the same thing, use netstat -nr and check out the resolver. And you
were all spot on!
For your interest, it was a weird problem. I have a small network linked to
the Internet via a 3Com ISDN router. This is the default gateway for the
network. The router masquerades my ISP-assigned IP address and this all
works fine. In order to do some learning, I added a Linux router (based on
the Linux Router Project stuff) attached to the network one side, and a
single Linux system on the other. I added a route to the ISDN router's
table so that packets for the Linux host would be directed to the router
interface. On the Linux host, I made the Linux router its default gateway.
Using a network analyser, I sniffed the packets. A ping to a numeric IP
address from one side of the network to the other worked fine. ICMP packets
for the Linux host were sent first to the ISDN router, which then sent them
to the Linux router. Hunky dory. But when I pinged from the Linux host to a
named host it screwed up. It sent DNS (UDP) request packets which reached
the DNS server, the DNS server replied (correctly) to the ISDN router, but
that sent back an ICMP "unreachable" packet. It seems unable to route UDP
or TCP back to the internal network properly when in masquerading mode. At
other sites I turn masquerading off and it works fine. Weird.
Anyway, for the purpose of the exercise I simply added routes on each of
the workstations, and it all works. Maybe I'll look at the ISDN router when
I have time...
Again, thanks for the very prompt assistance. It sent me straight to the
right area.
Neil
application/ms-tnef
