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 From:  "Braden McGrath" <braden at mcmail dot homeip dot net>
 To:  "Chris James" <lists at chrisjames dot me dot uk>, <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: [m0n0wall] Remote Desktop via NAT
 Date:  Sat, 7 May 2005 01:11:57 -0400
You generally shouldn't have to change MTU, especially not on cable.
What is your internet connection at HOME?  (Don't see it mentioned in
there.)  The only time MTU changes are needed is typically with a PPPoE
type setup, where you need to login to get to the internet.  It's much
more common with DSL than cable, at least in the US...

--Braden

-----Original Message-----
From: Chris James [mailto:lists at chrisjames dot me dot uk] 
Sent: Friday, May 06, 2005 4:27 PM
To: m0n0wall at lists dot m0n0 dot ch
Subject: [m0n0wall] Remote Desktop via NAT

Hi All,

This is a post with information for people searching the archives in the
future, born out of my frustration in trying to get remote desktop
working. My set up is:

* Windows Remote desktop (RDP) server (windows 2000 terminal server)
  behind a monowall 1.1 box doing NAT.
* m0n0wall with port 3389 forwarded from WAN to the internal IP of the
  server, and with the equivalent firewall rule in place.
* Remote computer #1 with direct leased line connection to internet
* Remote computer #2 via a NAT home router connected to Cable Broadband
  - in this case a D-Link DI-624+ connected to NTL in Leeds, UK

My symptoms were:

* Computer #1 (Leased line public IP) could connect perfectly to the
  Remote Desktop server
* Computer #2 (Cable, NAT) simply timed out on every connection with the
  error: "The remote connection has timed out. Please try connecting to
  the computer again."

Solution:

To cut a long story short... in the WAN settings of my D-Link router,
the MTU of the connection was set to 1500. By reducing it to 1400 it
works. Apparantly, remote desktop protocol has a problem with fragmented
packets, and obviously somewhere down the line, a router with a lower
MTU was fragmenting me.

Further info:

What is MTU? http://www.webopedia.com/TERM/M/MTU.html Changing the MTU
in D-Link routers:
http://support.dlink.com/faq/view.asp?prod_id=1297&question=General-Rout
ers
Changing the MTU with Dr. TCP on the client (note this was not required
for me - but I did use to get the 'safe' number of 1400):
http://kbserver.netgear.com/kb_web_files/n100603.asp Changing the MTU in
the registry: (again, not required by me - but possibly useful if you
have a similar problem, but have a machine directly connected to the
broadband network, not via a NAT router):
http://www.adslguide.org.uk/guide/mtu.asp

Hope this might help people with similar problems in the future.

Chris.
-- 
  Chris James
  http://www.chrisjames.me.uk


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