Cannot enable jumbo frames on vlan interfaces.

[sense]

Using single NIC (em0) physical box with Intel em driver and many vlans for testing. OPNsense 21.1-amd64

Originally em0 was left unassigned. All vlan sub-interfaces were assigned.
Setting vlan/OPT interface MTU to 9000 from Interfaces > Assignments page does not seem to work.
Adding em0 as an 'assigned interface' with 9000 mtu does not help.

I am able to apply the setting in web gui without issue, but unable to ping or route over 1500 MTU.

[sense]

Can anyone else confirm this issue?

[RedVortex]

Seems similar to this bug: https://github.com/opnsense/core/issues/4032 where I just added a comment at the bottom.

I can't enable jumbo frames anymore on my side either (21.1.4).

As soon as the vlan mtu and interface mtu are the same, it seems the vlan defaults to 1500 instead of what is configured in the UI. The interface is always applying properly however that is configured.

If I use different values on the vlan vs the interface it seems to apply properly however. Let's say I put 9000 on the interface (ix1) and 8999 on the vlan (ix1_vlan420), then the vlan uses the value and is now 8999. If I put back 9000 again on the vlan, it goes back to 1500 instead of 9000.

Just a hunch but it's probably just a logic error or something in the code when the interface mtu and vlan mtu match which then defaults to 1500 (or the mtu default value) instead of applying the config of the vlan.

The bug is "closed" for now since it "timed out" after 180 days. Maybe if a few persons comment in it they'll re-open and fix.

[Dragonfly]

I have the same problem. The physical NIC can be set to MTU 9000 fine, but the child VLAN interfaces can't. The GUI remembers the 9000 just fine, but when I check assignments (or via ssh: ifconfig), the MTU of the vlan interface is set to 1500.

I'm running 21.7, btw

[errored out]

Both of you may want to post to the github ticket as opnsense currently thinks this is an issue without that much impact.  The more people reporting on this issue, the more they will see a larger impact and be inclined to work on it.

[pmladenov]

Exactly the same problem ... I did exactly the same tests as the guy above (setting the MTU to 9000, 1500, 3000, 8999....). That's ridiculous, do I need a fresh install just because the requirement for jumbo MTU came a little bit late?

Of course ifconfig if_vlan mtu 9000 works, but not the buggy FrontEnd or BackEnd.... I'm start considering to install a native FreeBSD, or probably OpenBSD (because of the better pf implementation there, giving the options for active-active HA setups for both CARP and PF session replication) and stop using that peace of buggy scripts.