[Xen-users] Problem with the MTU in dom0

[Ralf Schmitt <ibm.tivoli@xxxxxxxx>]

Hello,

I'm wrestling with a problem with an untypical
"network device" ... an UMTS card that should
connect my notebook to the internet.

There is no problem with this card, when I
use a vanilla kernel but with the Xen kernel
I have to adjust the MTU to 400 (default is
1500) in dom0

  ifconfig ppp0 mtu 400

All other sizes don't work. My service provider
(e-plus Germany) wasn't able to help me, so
I've tried:

  - all other kind of MTU sizes
  - changed the TCP Maximum Segment Size (iptables)
  - disabled Path MTU Discovery
  - disabled compression in the kernel config
  - stopped the xen bridge

I build my dom0 kernels with:

    KERNELS ?= linux-2.6-xen0

in the Xen Makefile and I can't see any TCP or UDP
checksum errors in ethereal.


My questions:

  Could it be, that Xen changes something in the tcp
  header that I'm not able to see with ethereal?

    

Regards

  Ralf


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