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 From:  "Elijah Savage" <esavage at digitalrage dot org>
 To:  "Chris Buechler" <cbuechler at gmail dot com>, <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: [m0n0wall] Strangest Problem with VPN
 Date:  Sun, 27 Feb 2005 20:03:30 -0500
> All,
> 
> I need some help before I began pulling my hair out, here is the 
> situation.
> 
> M0n0wall-----Internet-----Cisco831
> 
> I have the tunnel up between these 2 devices and I know everything is 
> setup properly, as I can ping from one LAN subnet to the other. I can 
> also ssh from behind the LAN subnet of the monowall to the Lan subnet 
> of the 831. Now everyone is saying ok so what's wrong. Well when I try

> to RDP or send what seems to be any heavy traffic like RDP, file copy,

> etc it opens up the resources but never completes. Let me try to 
> explain better, like on a file copy I attach to the share it ask for 
> username and password I put it in and see the file share when I go to 
> copy it hangs up and locks up that session. If I RDP to a box from the

> monowall subnet to the other subnet it brings up the screen I put in 
> the username and password and it seems as if it is going to log me in 
> but just locks up the session.
> 
> Now from the 831 LAN subnet they can do anything they want to, it 
> looks as if they are sitting on my local subnet behind the monowall 
> they have no issues at all every service works great file sharing, 
> RDP, they can even print to my subnet. It seemed like a MTU issue at 
> first so I tried changing it on both sides and that did not make any 
> difference. I have taken all other access-list on the 831 off to make 
> sure it was not being caught by something else though I was sure it 
> wasn't and that did not make any difference. I did have a Cisco pix in

> place of the monowall and it all worked great but since you can't do 
> any traffic shaping on a pix I decided to try monowall. The traffic 
> shaping works great and I love it but now I am in a pickle because if 
> I can't get the vpn to work I will have to go back to the pix and give
up traffic shaping.
> 
> Any ideas or thoughts surely would be appreciated.

> Sounds like a problem with fragmented packets/MTU.  Solution?  I'm not
sure.  :)  It's one of many things I have on my > > list to figure out
and document troubleshooting and remediation procedures.

> Searching the archives for MTU might be helpful.  
>
http://www.google.com/search?q=mtu+site%3Am0n0.ch&sourceid=mozilla-searc
h&start=0&start=0&ie=utf-8&oe=utf-8
&client=firefox-a&rls=org.mozilla:en-US:official
>
> -Chris
>
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I have been working on this for 2 days and I figured it was a MTU issue
but have not found anything at all. Like I said I reduced the MTU on
both sides and it made no difference it is so frustrating. I sniffed the
packets and every packet sent from my LAN to the 831 LAN in ethereal it
says invalid checksome, I have recently swapped out the nic cards for 2
sis nic cards I had intel in the machine before. I wanted to buy a
soekris with vpn card but I think this will put a stop to that. I took
the monowall down today and put the pix in place and without no other
changes the vpn tunnel works fine and traffic flows both ways.