RE: Question regarding protocol specific mtu for FCoE

Zou, Yi
2009-06-03T22:22:28Z

>On Wed, 2009-06-03 at 13:43 -0700, Zou, Yi wrote:
>> >On Wed, 2009-06-03 at 12:16 -0700, Zou, Yi wrote:
>> >[...]
>> >> FCoE is on L2 layer, no path specific MTU, everything goes out as
>> >> whatever mtu known to the nic. Since the nic is expected to be
>used
>> >for
>> >> converged traffic involving multiple traffic types, e.g. LAN, FCoE,
>I
>> >> was wondering if it makes sense to have the additional MTU.
>> >Essentially,
>> >> the nic driver will be able to setup via netdev for different MTUs
>> >for
>> >> converged traffic.
>> >
>> >Wouldn't you use separate VLANs for FCoE and other traffic? So
>maybe
>> >we
>> >should allow for per-VLAN rather than per-protocol MTU.
>> >
>> >Ben.
>> >
>> From what I can tell, you will not be able to set vlan device's MTU
>> that is larger than the real_dev->mtu, as in vlan_dev_change_mtu().
>
>Yes, I know this restriction exists at the moment. But the device MTU
>(the limit for dependent virtual devices) could perhaps be decoupled
>from the interface MTU (the limit for protocols) and automatically
>raised when necessary. I think something like that is necessary for
>your proposal too.
>
>Ben.
Well, for all all NIC devices that are capable of doing converged
traffic, the additional MTU seems to me fits just what you mentioned as
the automatic MTU increase, since a different MTU is checked. Of course,
the vlan above needs to be also fixed to allow this as well. Also, FCoE
should not required to be created only on a VLAN interface.

Thanks.

yi