Re: [uml-devel] question about udp fragmentation under UML

["Yari Adán Petralanda" <mustang@yadan.org>]

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Hi again,

Problem solved with 2.6.9 vanilla and 2.6.9-bb4. Thank you very much for your 
answer, and sorry for not testing it on the latest kernels before. I thought 
there were no new versions when I saw 2.6.8.1 last on the website. Didnt knew 
2.6.9 works right out of the box,

Thank you again

El Miércoles, 19 de Enero de 2005 22:54, escribió:
> On Tuesday 18 January 2005 07:28, Yari Adán Petralanda wrote:
> > Hi,
> >
> > I'm developing a network block device, which uses both TCP and UDP
> > sockets to transmit it's data. When I try to send UDP frames bigger than
> > the MTU, they are dropped before they hit the wire.
>
> This exact problem (a checksum corruption in fragmented UDP packets) was
> already debugged and solved, and even vanilla 2.6.9 includes the fix...
> currently the recommended tree is 2.6.9-bb4 on my homepage.
>
> I assume that you should first try 2.6.9-bb and, if you still have
> problems, ask again... Anyway please post an ack about whether 2.6.9-bb
> solves this bug, ok? Thanks.
>
> > Trying to debug the problem, I
> > ran netcat using udp under a UML. It uses writes of 8192 bytes over a UDP
> > socket. The scenario that made me post here is this:
> > running UML on tracing thread mode, host kernel is 2.6.10, uml kernel is
> > 2.6.8.1-1um,
> >
> > if I set the MTU of the localhost device (same problem on
> > tun/tap) to 1500 bytes, netcat doesn't receive any frames sent to the
> > loopback interface. path_mtu_no_discover is 0. The same scenario, on my
> > host computer, runs fine.
> >
> > Seems to me that IP is refusing to fragment the udp datagrams, and drops
> > them.
>
> I've debugged this with ethereal and the result was that the checksum, in
> the case of fragmented packets, was wrong - so the receiving side dropped
> the packets...
>
> Bye

-- 
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    oo|    Yari Adán Petralanda, a.k.a. mustang
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  (\_;/)           http://www.yadan.org
              Registered Linux User #257290                     
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