WAN PPPoE does not respect setting MTU >1492 (RFC4638)

[fbantgat7]

With WAN configured to use PPPoE and my ISP accepting 'baby jumbo' frames larger than 1500 octets, I used to be able to set MTU=1500 on WAN-pppoe0, which would increase the NIC port to an MTU of 1508.

After an upgrade some versions ago I realised this approach would no longer work.  The NIC MTU remained at 1500 and connections to the Internet (including this site) broke.  As a manual workaround I ended up using the console to increase the NIC port to 1508 with ifconfig, which would trigger a renegotiation and consequently the WAN interface would auto-adjust up to an MTU of 1500.

With the latest upgrade to OPNsense 23.1.6 I am no longer able to do this.  Using ifconfig to increase the MTU of the NIC to 1508 does not auto-adjust the WAN pppoe0 MTU to 1500, it stays at 1492.  Using ifconfig subsequently to increase the pppoe0 MTU to 1500 manually works, as far as the ifconfig console output and the GUI interface shows.  However, ping tests show the pppoe0 MTU remains at 1492.

Is this a known problem?

Is there a way available to negotiate WAN-pppoe0 frames with an MTU of 1500?

EDIT:  Oops! Another test shows the pppoe0 MTU does increase.  Perhaps it hadn't renegotiated with the ISP when I tried it last time.

[Taunt9930]

You have to go to interfaces > assignments, then assign the physical WAN port (e.g. igb0, for example) to a new interface (it is not assigned by default). I called mine 'ignore'. You can then edit the interface, and merely set the MTU of that interface to 1508 in the UI - no need to set anything else. Save, then it will allow a 1500 MTU setting to work on the 'WAN'/pppoe interface

[fbantgat7]

Thanks Taunt9930, I'll try this next if manually editing on the console doesn't work.