I think it is helpful to tell the user what happens if the remote endpoint doesn't support RFC 4638.
OK? - todd Index: share/man/man4/pppoe.4 =================================================================== RCS file: /cvs/src/share/man/man4/pppoe.4,v retrieving revision 1.34 diff -u -p -u -r1.34 pppoe.4 --- share/man/man4/pppoe.4 16 Jun 2017 10:58:43 -0000 1.34 +++ share/man/man4/pppoe.4 16 Mar 2021 12:05:40 -0000 @@ -201,6 +201,14 @@ With this, the previously mentioned MSS .Xr pf.conf 5 are no longer necessary. .Pp +If you attemp to use an MTU larger than 1492 where the remote equipment does +.Em not +support RFC 4638, +.Nm +will write +.Dq No valid PPP-Max-Payload tag received in PADO +to the kernel message buffer and the MTU will be clamped to 1492. +.Pp See .Xr pf.conf 5 for more information on MTU, MSS, and NAT.
