pfSense

I have a setup with a Multi-WAN configuration, with one cable modem with MTU 1500 and one DSL modem, MTU 1492. After a bit of Wiresharking, I realized this and set the interface MTU on the DSL side, but then realized clients needed this setup as well, and finally discovered DHCP option 26 and set that to 1492, and now all is great.

To make this easier for the next guy, it would be lovely to have a checkbox inside the DHCP Server configuration, such as:

[X] Set DHCP interface MTU option to lowest WAN interface value

Having that as a default, even, would improve ease-of-use. I don't yet know how to do path MTU discovery on WAN interfaces, but if that's possible, with this option the whole mess could be plug-and-play.