🚀 go-pugleaf

(Apologies for cross-posting to demon.ip.support although this is mostly 
OS specific, but dis.nt seems to be dead. Also although this is a home 
network, it probably isn't a typical home network.  Advice on other 
better groups is welcome)

I am having serious problems with the routing between my internal 
network and the Internet and need some advice on troubleshooting.

My set up is as follows.

I have a W2K server with a cable modem and an ISDN card. I have a number 
of other machines on an Ethernet network (W2K Professional and Linux) 
which use the W2K server as a gateway.

The cable modem appears to W2K as an Ethernet port and gets its IP 
configuration, including default gateway and DNS servers via DHCP from 
the cable provider.    I have set up network address translation on the 
W2K machine and set the default gateway on the other machines to the W2K 
machine.

This all worked perfectly until the other day when I tried to set up a 
demand-dial interface on ISDN so I could collect mail and news from my 
ISP (Demon) using dial-up (you have to dial-up to demon to use their 
mail and news).  This seemed to work initially but then started to fail 
intermittently.  I took out the demand dial interface, but the problems 
persisted.

The situation now is that external connectivity from any of my 
workstations is up and down like a yo-yo.  The situation can change from 
second to second but as far as I can tell, by turning round and doing 
the same thing on the gateway machine, the problem is internal rather 
than external (although of course by the time I turn round the situation 
may have changed).

I have a number of ideas about possible causes, but am at a loss on how 
to investigate further. I need some guidance on tools and techniques to 
try to pin it down.

One potential problem is either the reliability of, or routing to, my 
providers DNS servers.  Is there a set of alternative DNS servers I can 
use to help distinguish? Can I use demon DNS servers when not dialled up 
to demon?

How can I pin down the routing problem to internal or external?

If it is internal how can I diagnose the cause in the W2K server?





-- 
Jim Smith