Bug 15777

Summary:	Changing MTU after enabling GSO/GRO breaks incoming IPv6 neighbour discovery
Product:	Networking	Reporter:	Roman Mamedov (rm+bko)
Component:	IPV6	Assignee:	Hideaki YOSHIFUJI (yoshfuji)
Status:	RESOLVED OBSOLETE
Severity:	normal	CC:	alan, higuita
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	2.6.33	Subsystem:
Regression:	No	Bisected commit-id:

Description Roman Mamedov 2010-04-13 16:17:38 UTC

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.

Comment 1 Andrew Morton 2010-04-13 19:38:36 UTC

(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@bugzilla.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@linux-ipv6.org
>         ReportedBy: roman@rm.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.

Comment 2 Alan 2012-11-20 17:20:20 UTC

Closing as obsolete, if this is still seen with modern kernels please re-open and update