Re: [LARTC] Gre Tunneling Problem

[Christoph Simon <ciccio@kiosknet.com.br>]

On Mon, 7 Jan 2002 17:40:47 +0800
"glynn" <glynn@itextron.com> wrote:

> when you configure that tunneling did you reconfigure your kernel? what
> should i enable in my kernel? by the way when i log-on to the linux A, I
> could ping the linux B eth0(internet) and eth1(let say "192.168.1.1")
> but when i ping the "192.168.1.2" which is a windows workstation
> connected to hub it wont pass thru. how do i sniff the interface where
> the packets go, can you help me about that pls. Thanks

So you can ping from 192.168.2.1 to 192.168.1.1, this is good, as it
means that the tunnel definitively is working.

Now, if you try to ping from 192.168.2.1 to 192.168.1.2, the Windows
box, it seems to fail. First I would try to ping from 192.168.1.1 to
192.168.1.2, just to make sure, everything is working fine locally. If
this works too, I would make tcpdump listen at the external interface
of 192.168.2.1. Does the packet actually go out? If not, the routing
or filter problem must be there. If it works, I'd listen on the
external interface of 192.168.1.1; obviously these must arrive because
the tunnel is working and the packet left at the other side. Now you
can listen to the internal interface, seeing if the packet is actually
being forwarded. If this fails, your problem is routing, filtering or
forwarding on 192.168.1.1. Don't know how to sniff on a Windows, but
as the ping from 192.168.1.1 to 192.168.1.2 presumibly worked, there
shouldn't be a need.

If you have access and there is no other traffic, a much simpler
method would be just to watch the leds on the modems, network cards,
hubs, etc. This will help finding out where your problem is. As you
can ping the first computer after the tunnel, I feel sure, the tunnel
is working fine, the problem must be in another place, probably a
stupid little detail.

Note that the suggestion of introducing a different network address
for the tunnel interfaces themselves will slightly complicate
routing. But if you pay attention, this shouldn't be a problem.

-- 
Christoph Simon
ciccio@kiosknet.com.br
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