Re: tap mtu limitation

[Edward Chapman]

Yes I found out that from 2.6.24 its now possible to change the mtu on
tap interfaces.  I was running 2.6.23 when I first wrote my message :)

For anyone interested look at the git history for the tun.c file in the
kernel there is a commit which introduces ability to set higher mtu in
2.6.24

regards,
Eddie

On Fri, 2008-03-28 at 11:33 +0100, Jiri Olsa wrote:
> No sure what you use, but this works for me in 2.6.24.3:
> 
> emnote linux-2.6-stable # tunctl -t tap0
> Set 'tap0' persistent and owned by uid 0
> emnote linux-2.6-stable # ifconfig tap0 mtu 2000
> emnote linux-2.6-stable # ifconfig tap0
> tap0      Link encap:Ethernet  HWaddr 00:FF:8D:16:53:9A  
>           BROADCAST MULTICAST  MTU:2000  Metric:1
>           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:500 
>           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
> 
> 
> regards,
> Jiri Olsa
> 
> Edward Chapman wrote:
> > tap devices appear not to support an mtu higher than 1500:
> > 
> > usilap:/ # uname -r
> > 2.6.23.12
> > usilap:/ # /usr/bin/tunctl -u root -t tap0
> > Set 'tap0' persistent and owned by uid 0
> > usilap:/ # ip link set tap0 mtu 1500
> > usilap:/ # ip link set tap0 mtu 1501
> > SIOCSIFMTU: Invalid argument
> > usilap:/ # ip link set tap0 mtu 1600
> > SIOCSIFMTU: Invalid argument
> > 
> > Would it be trivial to remove this limitation?  Can anyone tell me where
> > is the code that is enforcing this limitation?  Is it in
> > drivers/net/tun.c ?
> > 
> > thanks,
> > Eddie
> > 
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