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To: "Mark Smith" <mark.smith,AT,avcosystems,DOT,co,DOT,uk>
Subject: Re: Linux <-> Win2k issues
From: "Hans Steegers" <J.Steegers,AT,chello,DOT,nl>
Date: Fri, 2 May 2003 14:14:58 +0200
Cc: <cipe-l,AT,inka,DOT,de>
Reply-to: "Hans Steegers" <steegers,AT,steegers,DOT,nl>

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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