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To: <cipe-l,AT,inka,DOT,de>
Subject: RE: Linux <-> Win2k issues
From: "Mark Smith" <mark.smith,AT,avcosystems,DOT,co,DOT,uk>
Date: Fri, 2 May 2003 14:40:31 +0100
Importance: Normal
In-reply-to: <004201c310a4$737c1ae0$d61fa8c0@pcw_hans.hnsasd.priv>

If it's not inappropriate, can I ask - when people reply to messages, can
they send them only to the list please?  I get two copies when messages are
sent to both my address and the list, I'm sure others probably do as well.

In reply,

The VNC connection generates these (output from tcpdump):

13:51:20.052270 starbug.avco > cdc.avco: icmp: starbug.avco unreachable -
need to frag (mtu 1442) [tos 0xc0]

However, this connection works.  My question about about the MTU, which this
specific log entry does indeed mention, might be related to the problem with
the win32 adaptor reporting a higher mtu than it should.  DKW - do you have
any ideas as to if or when a patch might be released with this fixed even if
only in the interim?

Mark Smith - Avco Systems Ltd
email: mark.smith,AT,avcosystems,DOT,co,DOT,uk
Tel: +44 (0)1784 430996 Fax: +44 (0)1784 431078

-----Original Message-----
From: owner-cipe-l,AT,inka,DOT,de [mailto:owner-cipe-l,AT,inka,DOT,de Behalf 
Hans Steegers
Sent: 02 May 2003 13:15
To: Mark Smith
Cc: cipe-l,AT,inka,DOT,de
Subject: Re: Linux <-> Win2k issues

Your problem with vnc is most likely caused by your firewall: vnc needs icmp
for routing purposes.
When icmp packets type 3 (destination unreachable) are blocked, vnc behaves
as described: It connects, authenticates and the screen stays gray (initial
screen loading..) or disconnects after some time. Allowing ICMP solves this

Hans Steegers

-----Oorspronkelijk bericht-----
Van: Mark Smith <mark.smith,AT,avcosystems,DOT,co,DOT,uk>
Aan: Cipe list (E-mail) <cipe-l,AT,inka,DOT,de>
Datum: vrijdag 2 mei 2003 13:32
Onderwerp: Linux <-> Win2k issues

>Having finally gotten around to testing my setup, and having gotten most of
>it operational, I have a few questions that hopefully may already have been
>answered; sadly searching for likely keywords hasn't found me the relevant
>After setting up the tunnel itself and proving that traffic passes between
>the two machines, I've extended it slightly to allow access to other
>machines connected to the linux end.  Specifically, the default route for
>the Win2k side is the linux end of the tunnel, and the linux end has an
>iptables rule to SNAT outbound traffic in POSTROUTING to it's own IP
>to ensure return traffic gets routed correctly.
>This works perfectly, at least at first glance.  I can ping and telnet and
>the traffic gets passed over and through as I would expect.  However,
>although I can map network drives to Windows machines on the linux end, I
>keep getting large amounts of messages in the logs:
>May  2 12:19:26 starbug kernel: cipcb0: got short packet from <win2k ip>
>May  2 12:19:56 starbug last message repeated 3 times
>May  2 12:19:58 starbug kernel: UDP: bad checksum. From
> ulen 214
>May  2 12:20:08 starbug kernel: cipcb0: got short packet from <win2k ip>
>May  2 12:20:48 starbug last message repeated 4 times
>I also can't seem to get a vnc connection to display at all, eventually
>resulting in a read error.  It connects, authenticates the password, and
>a little while I can see the mouse moving around on the host, but the
>remains blank.
>My suspicion at this point in time is packet size, either too small, too
>large (ie close to or greater than MTU) or a size mismatch; perhaps the
>being stored or reported is not the actual size being used, I don't know
>Please, ask questions if there's some information you want me to provide in
>order to try to resolve this problem.  The vnc connection is the reason for
>setting this whole thing up, so at the very least I could do with that
>Thanks in advance,
>Mark Smith - Avco Systems Ltd
>email: mark.smith,AT,avcosystems,DOT,co,DOT,uk
>Tel: +44 (0)1784 430996 Fax: +44 (0)1784 431078
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