netdev - Re: [Bugme-new] [Bug 15777] New: Changing MTU after enabling GSO/GRO breaks incoming IPv6 neighbour discovery

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Date:	Tue, 13 Apr 2010 12:37:31 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	netdev@...r.kernel.org
Cc:	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, roman@...pp.ru
Subject: Re: [Bugme-new] [Bug 15777] New: Changing MTU after enabling
 GSO/GRO breaks incoming IPv6 neighbour discovery


(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Tue, 13 Apr 2010 16:17:44 GMT
bugzilla-daemon@...zilla.kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=15777
> 
>            Summary: Changing MTU after enabling GSO/GRO breaks incoming
>                     IPv6 neighbour discovery
>            Product: Networking
>            Version: 2.5
>     Kernel Version: 2.6.33
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: IPV6
>         AssignedTo: yoshfuji@...ux-ipv6.org
>         ReportedBy: roman@...pp.ru
>         Regression: No
> 
> 
> I have discovered that on one machine, if I enable either GSO or GRO (with
> ethtool -K), and then change the interface MTU, the machine ceases to be IPv6
> neighbour-discoverable. After the following commands:
> 
>   ethtool -K eth0 gro on gso on # doesn't matter which of them, or both
>   ifconfig eth0 mtu 4082
> 
> the machine is no longer ping6'able from LAN by "new" hosts (which haven't seen
> it recently) -- until something ELSE is adjusted on the same interface of that
> machine, e.g. the following command helps (I don't know why, the PROMISC mode
> is already disabled when it runs):
> 
>   ifconfig eth0 -promisc
> 
> The NIC (using the "skge" driver):
> 
>   00:08.0 Ethernet controller: 3Com Corporation 3c940 10/100/1000Base-T
> [Marvell] (rev 10)
> 
> The system is a  Debian Squeeze with 2.6.33 kernel and ethtool 2.6.33.
> 
> The issue is 100% reproducible.

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