[Gllug] Path MTU and multiple layers of NAT -- bad?

[Richard Jones]

On Wed, Feb 08, 2006 at 02:29:00PM +0000, Daniel P. Berrange wrote:
> On Wed, Feb 08, 2006 at 02:39:58PM +0000, Richard Jones wrote:
> > 
> > I've got a strange case where I can't fetch web pages from a remote
> > server.  I can ping the server, I can connect to the remote server,
> > but after that the connection hangs until close.
> > 
> > The difference seems to be that (for various reasons) I'm trying to
> > connect over multiple (3) layers of NAT.  My best guess is that path
> > MTU discovery is screwed up somehow.
> 
> > Any ideas or further things I can try?
> 
> Having PMTU disocvery enabled, means that all packets will be sent with
> the DF bit set, so to test if this is the problem temporarily disable 
> PMTU and let the packets fragment normally.
> 
>   echo 1 >  /proc/sys/net/ipv4/ip_no_pmtu_disc 

Right, well, turns out that PMTU discovery *isn't* the problem in that
case.  Any further ideas ?!?

It's very strange that it can ping, can manage the 3-way handshake,
but can't send a packet with a 16 byte payload.

Tracing from the web server end indicates that the packet with the 16
byte payload is never received.

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com
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