RE: [Sheflug] SuSE 7.3 Network Problems

[Alex Hudson <xxxxx [at] xxxxxxxxxxxxxx>]

On Sat, 2001-12-15 at 11:05, Alistair Williamson wrote:
> I am also running SuSE 7.3 on my laptop - when it's connected to the
> network - it can exchange pings with all the other machines (except the
> server!)

Okay, it's not firewall.

First, let's rule out hardware. You've tried different cards, so it's
not the card that's the problem. Swap cables with a known working node
on your network (assuming you have more than one other PC on this
network), and try with that. If it still doesn't work using the
connection that works for other machines, then it's not hardware at all.
If it does work, it's either a dodgy cable or a dodgy port on your hub.

In terms of software, there are a number of things it could be. The best
thing to do is make use of virtual terminals - I would run (as root)
'tcpdump -i eth0 -n' on a terminal and leave it running while you test
the network on a different terminal - this way, you're capturing all
your network stuff which may help sort out why this isn't working.

Try pinging again while capturing data. You should see a line like this:

11:18:28.780776 192.168.0.1 > 192.168.0.10: icmp: echo request (DF)
11:18:28.780888 192.168.0.10 > 192.168.0.1: icmp: echo reply

(That's my gateway machine pinging my laptop). Ignore the numbers at the
start of the line. What you're interested in is the other stuff:
generally, it's:

	IP address A > IP address B: traffic

So the machine at 'a' is talking to 'b', tcpdump will also tell you
roughly what they're saying. If you see something which looks like a
five-tuple IP address (i.e., something like 192.168.0.10.80) the last
number is the port.

Now, if your network _really_ isn't working, all you're going to see is
something like:

11:22:40.598992 arp who-has 192.168.0.10 tell 192.168.0.1

.. with no responses. If this is all you get, then something's really
screwed - I would guess hardware, but hopefully you've ruled this out,
so this would probably indicate drivers (but this would be _very_
surprising). If you see anything more than just this, then your network
is running at some level.

Things to try:

	ping -n (some valid ip)   - you know what this does ;)
	arp 			  - the output of this would be useful; 
				    it should be the MACs of the other
				    network machines.

Make sure you're using the -n option on ping. Make sure you're not using
the same ip address elsewhere (always worth checking ;). Make sure the
network configuration (subnets, etc.) is the same on the other machines.

Cheers,

Alex.


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