[c-nsp] q-in-q mtu

[Christophe Lucas]

Le 21/10/2010 11:21, Antonio Querubin a écrit :
> On Thu, 21 Oct 2010, Daniel Hooper wrote:
>
>> I was under the impression that interfaces handling Q-in-Q needed
>> atleast an MTU of 1504 bytes.
>
> The 7206 doesn't accept anything higher than 1500 on that interface.
>
> I did some testing with the carrier today and we found that 1490 was the
> highest MTU that would reliably allow web browsing.  One would think that
> 1496 or 1492 would do the trick but 1492 didn't make a difference.  There
> was some useability at 1491.
>
> Antonio Querubin
> 808-545-5282 x3003
> e-mail/xmpp:  tony at lava.net
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>

Hi,

On this kind of router :

core4.rou01#sh ver | inc IOS
IOS (tm) 7200 Software (C7200-P-M), Version 12.3(19), RELEASE SOFTWARE (fc2)
This Version of Cisco IOS Software is not supported on NPE300.
Please select a version of Cisco IOS software compatible with
core4.rou01#sh run int gi 0/0
Building configuration...

Current configuration : 167 bytes
!
interface GigabitEthernet0/0
  mtu 1530
  ip address x.x.x.x 255.255.255.252
  duplex full
  speed 1000
  media-type gbic
  negotiation auto
  tag-switching ip
end
core4.rou01# ping y.y.y.y si 1520

Type escape sequence to abort.
Sending 5, 1520-byte ICMP Echos to 217.169.255.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
core4#

You could be able to set mtu higher than 1500, so that you can handle 
q-in-q frames.

<off topic>
I am interested in what kind of router are terminating your Q-in-Q vlan ?
</off>

-- 
Christophe Lucas - Network Engineer - c.lucas at infosat-telecom.fr
Tel : +33(0)974.762.595 - Fax : +33(0)09.72.19.53.58