Re: tap mtu limitation

[Jiri Olsa]

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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