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Bug#851825: ethtool: ifdown/ifup sequence fails if offload_tx off is set in iface stanza

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On Wed, 30 Aug 2017 10:24:52 +0200 Daniel Reichelt <debian@nachtgeist.net> wrote:
> On 08/30/2017 12:18 AM, Ben Hutchings wrote:
> > I can't reproduce this.  What driver is used for eth0 (ethtool -i shows
> > this)?
> 
> Ben,
> 
> you're on to something:
> 
> 
> # ethtool -i eth0
> driver: vif
[...]
> Indeed, this only happens in XEN guests running on a jessie host (didn't
> get around yet to test whether a stretch host makes the difference).
> 
> On any other hw I own (a couple of e1000e and a r8169), ethtool always
> exits 0, with changes to offloading having been made or not.
> 
> Sorry for not mentioning the fact about VMs earlier...just didn't think
> of it.

Returning to this at last… the problem is that the xen-netfront/vif
driver always enables TX checksum offload for IPv4 and only allows it
to be controlled for IPv6.  That might be a bug in the driver or just a
limitation of the Xen PV networking protocol.

Initially the interface has TX checksum offload enabled for IPv4 only.
Running "ethtool -K tx off" can't disable it for IPv4 (failure), but
running "ethtool -K tx on" does enable it for IPv6 (success).

Running "ethtool -K tx on" and then "ethtool -K tx off" succeeds, but
still has no effect on TX checksum offload for IPv4.

I don't see this as a bug in ethtool.

Ben.

-- 
Ben Hutchings
For every complex problem
there is a solution that is simple, neat, and wrong.

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Bug#851825: ethtool: ifdown/ifup sequence fails if offload_tx off is set in iface stanza Ben Hutchings <ben@decadent.org.uk> - 2020-01-30 18:20 +0100

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