Re: Increase mtu? How?

Jan Klemkow <[email protected]>
Newsgroups gmane.os.openbsd.misc
Message-ID <[email protected]>
On Fri, Jun 05, 2026 at 12:43:35PM +0200, Thomas Pries wrote:
> Am 05.06.26 um 00:09 schrieb David Gwynne:
> > On Thu, Jun 04, 2026 at 10:52:10AM +0200, Thomas Pries wrote:
> > > ...
> > > ifconfig ix0/ix1?? hwfeatures ...??hardmtu 9198
> > > ifconfig aggr0?? hwfeatures ...??hardmtu 9198
> > > ...
> > OpenBSD is different to most other systems in how it handles packet
> > sizes and MTU on interfaces. ...
> 
> Thank you very much for this detailed explanation.
> 
> My network college would be happy, if I could would set the MTU to 9180 and
> I tried to set this on aggr0 and ix* via:
> 
> ifconfig ix0 down
> 
> ifconfig ix0 mtu 9180
> 
> but I always get the error:
> 
> ifconfig: SIOCSIFMTU: Device busy
> 
> What is the procedure to set the MTU?

As David already said:

> In your set up it's the MTU of the vlan interfaces that matters, but
> only to the IP stack. Everything underneath it is already set up for you
> to be able to increase the MTU on the vlan interfaces.

So, this should do it for you:

ifconfig vlan1002 mtu 9180
ifconfig vlan689 mtu 9180

bye,
Jan
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