Re: vlan with higher MTU (jumbo frame) than underlying Ethernet interface

[Matt Thomas <matt%3am-software.com@localhost>]

On Sep 7, 2012, at 1:17 PM, Erik Fair wrote:

> 
> On Sep 7, 2012, at 12:53, Manuel Bouyer wrote:
> 
>> On Fri, Sep 07, 2012 at 11:21:11AM -0700, Erik Fair wrote:
>>> NetBSD's documentation doesn't say explicitly: can one have a vlan 
>>> interface with a jumbo frame MTU (e.g. 9000), on top of an Ethernet 
>>> interface which supports jumbo frames, but whose MTU (1500) has not be 
>>> adjusted up?
>> 
>> No, I think the underlying interface needs to have the hightest MTU of all
>> vlans.
> 
>> But you can have another vlan(4) interface with 1500 MTU
> 
> Unfortunately, that's backwards: for network booting (SFAIK, no system 
> firmware supports or uses jumbo frames - it's an unsafe assumption), and for 
> systems that don't support jumbo frames to be on the same LAN, you need those 
> to be on the non-vlan'd network (no VIDs) and everything configured so that 
> no one sends or broadcasts any packets to them bigger than the standard MTU.

set the mtu on the interface route.