PPPoE Jumbo Frames appears to be broken MTU

[LogicEthos]

After updating to 19.1.9, a lot of web pages refused to load, yet I could ping out.  It was an MTU issue.

For 1500 MTU over PPPoE, I had the MTU set to 1508, which has worked until now.

[AdSchellevis]

which version did you upgrade from?

Can you also check the output of the following command:

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grep mtu /var/etc/mpd_*.conf

It should show and mtu as the value set in the interface minus 8 (1508 --> 1500), which it seems to be doing in my case, but I don't have an actual pppoe to test.

[LogicEthos]

I updated from the previous version. 19.1.8

I now have it set to 1500 which works (albeit at the lower MTU), and it is showing 1492 as expected.
I cant change is back to 1508 right now, as the network is in use.  But I will try later.

Looking through my bash history from yesterday, I saw this in the ifconfig

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pppoe0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> metric 0 mtu 1500
So it looks like it's being set.

[LogicEthos]

So I now set it to 1508, and it fails again.

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grep mtu /var/etc/mpd_*.confReturns nothing.

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set console close
  # configure the web server
  set web close

default:
pppoeclient:
  create bundle static wan
  set bundle enable ipv6cp
  set iface name pppoe0
  set iface route default
  set iface disable on-demand
  set iface idle 0
  set iface enable tcpmssfix
  set iface up-script /usr/local/opnsense/scripts/interfaces/ppp-linkup.sh
  set iface down-script /usr/local/opnsense/scripts/interfaces/ppp-linkdown.sh
  set ipcp ranges 0.0.0.0/0 0.0.0.0/0
  set ipcp enable req-pri-dns
  set ipcp enable req-sec-dns
  create link static wan_link0 pppoe
  set link action bundle wan
  set link disable multilink
  set link keep-alive 10 60
  set link max-redial 0
  set link disable chap pap
  set link accept chap pap eap
  set link disable incoming
  set pppoe max-payload 1500
  set auth authname "XXXXXX"
  set auth password XXXXXXX
  set pppoe service "XXXXX"
  set pppoe iface em0
        open

Set it back to 1500

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/var/etc/mpd_wan.conf:  set link mtu 1492
Looks like this is the same problem https://forum.opnsense.org/index.php?topic=11733.0

[LogicEthos]

I found the problem.
I un-ticked  "Prevent interface removal" on the WAN interface.