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Re: [Xen-users] bad udp checksums

Hi Mike,

2012/3/22 Mike Wright <mike.wright@xxxxxxxxxxxxxx>:
> Hi all,
> I'd hoped this had gone away but discovered that ntp is failing because of
> this (fortunately dns seems to ignore the bad sums and answers anyway).
> Basic info:
> xen-4.1.1 compiled locally
> linux 3.0.0 compiled locally
> fedora 14
> I ran "pethtool -K {all interfaces, all bridges, doms} tx off" with no
> apparent effect.
> I found an old email about xen-3 where somebody had patched this file:
>   "xen/netback/interface.c"
> this way:
>   -    dev->features        = NETIF_F_NO_CSUM;
>   +    dev->features        = 0; /* replaced NETIF_F_NO_CSUM */
> to eliminate the symptom but I don't think that really solves the underlying
> problem.
> Open for any advice or suggestions.

Linux must correctly start computing/checking checksums if the
underlying device reports it's not supporting hw checksumming.
At some time I read that Linux doesn't generally verify checksums. I
don't know if it's true.
First thing to look into though - find out if it's true and how to
enable checksum verification on the receiver.

Second thing - I don't think many people are seeing any issue like
this anymore these days. Try replacing the NICs for a test (also just
working around the symptoms instead of properly computing checksums,
yes. But there's NICs with broken FW and there's NICs with non-broken

Last thing would be to switch to virtual function nics and pci delegation.

I'll take to crying if nothing else helps.

OR HOPEFULLY, someone else knows more about this!


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