In message <200010251905.e9PJ5Oa24142@flash.vaultron.com>Andrew Gillham writes

[...]
>> 1496? Say what? You mean somebody *broke* Ethernet on non-VLAN-capable
>> interfaces?  I really hope not.
>
>No, the MTU in question is on the vlan interface after attaching it
>to the parent.  If the parent doesn't support the larger vlan mtu then
>the vlan interface ends up 4 bytes less than the parent MTU. (or is
>it hard coded to 1496?)


Oh. thats the source of the confusion, then.  I think what people were
asking for is somethign different: a way to query an interface, to
find out if it can do full VLAN or not, *before* you try configuring
a VLAN interface on it.

Personally, I dont see the point of trying to do "vlan" with a 1496
MTU;; thats as broken as FDDI-to-Ethernet "bridges", for much the same
reasons, and with much the same gotchas and failure modes.

But if people think its useful, who am I to argue with them? :-;.