Re: [Xen-users] bad udp checksums

[Florian Heigl <florian.heigl@xxxxxxxxx>]

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
FW)

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!

Florian

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