Networking help

[pll at lanminds.com]

In a message dated: Tue, 26 Nov 2002 21:50:56 EST
bscott at ntisys.com said:

>On Tue, 26 Nov 2002, at 8:23am, pll at lanminds.com wrote:
>>> Is the system multi-homed?  If so, is there any chance it is sending the
>>> packets out the wrong interface?
>> 
>> Yes it is multi-homed, that's how I ssh to it.  I ssh to systemB on 
>> it's external interface, then to C on the internal interface.
>
>  I meant: Is systemC multi-homed?

Err, yes.  This was all specified in the original post, of course, I 
don't think anyone has that around anymore at this point ;)

All systems on that subnet are multihomed, systemB and systemC.


>I was wondering if systemC is sending an
>ICMP echo reply on an interface you're not paying attention to.

No, I checked that, I had one window to systemC 
open for each interface and ran tcpdump on a specific interface.  The 
only interface receiving icmp echo requests was the "public" 
interface I was actively pinging from systemA (my desktop).

>I don't even recall what systems A and B were doing in your description.
>I was focusing on the single fact that systemC is apparently
>receiving ICMP echo requests without responding with an echo reply.
>That is a well-delineated problem.

That is *the* problem.  systemA is my desktop on a subnet different 
from that of systemC.  SystemA is pinging systemC.  SystemC is 
receiving but not replying to the echo request.

SystemB is a system on the same subnet as systemC which I can use to
get access to systemC via a private/non-routed subnet they are both 
connected to.  This is how I ran tcpdump on systemC.

>wildfire# tcpdump -i eth0
>tcpdump: WARNING: eth0: no IPv4 address assigned
>tcpdump: listening on eth0
>
>  (I am not sure that is useful, but I find the fact that it works
>interesting.  :)

My point was, for an interface which is not configured, you'll likely 
not see any traffic :)  And yes, it is interesting that it does work!

>  Given your description of variances between nearly-identical systems, you
>might also consider the possibility that the OEM of your systems had a bad
>run of network interface controllers.  A marginal IC might induce
>intermittent, single-bit errors that would be very hard to track down.

True, and something I have definitely considered.  Of course, I 
haven't had any time these past two days to continue this 
investigation, so I don't even know if the problem is still occurring!
-- 

Seeya,
Paul
--
	It may look like I'm just sitting here doing nothing,
   but I'm really actively waiting for all my problems to go away.

	 If you're not having fun, you're not doing it right!