[HowTo] - PPPoE, VLAN & RFC4638

[Taomyn]

So if I understand this correctly and I already have my PPPoE set up and that hopefully my ISP supports this, all I need to do is adjust the MTUs at the same places? I don't have one for VoIP so I can just adjust things for the two interfaces.

[joeyboon]

Thanks! This post made me realize I needed to enable the phisical interface in order to change the MTU to 1508 (in my case). I thought I already implemented rfc4638 by changing the settings on the WAN interface (vlan). Thanks again! 

[furfix]

Sorry for bring this up after so many time, but this config works if the ISP also provides IPv6?

[RamSense]

thanks for this detailed guide. Does this stil work on OPNsense 23.7.3-amd64
I have configured it like you did and WAN_FTTH MTU 1508, but at interfaces-overview I still see: MTU 1492 ?

A reboot did not help either.

[franco]

It's being worked on at the moment. I assume some sort of driver prevents to change the MTU... but it's not easily reproducible. Legend has it the development version already works, but only one person did confirm this briefly.


Cheers,
Franco

[RamSense]

Thanks Franco for the fast reply and good to know, while waiting the next update :-).

[franco]

Depending on the lack of feedback on the development version the stable rollout will likely be paused as well.

So we talk about some time in October perhaps.


Cheers,
Franco

[RamSense]

is there a patch I can run to check on OPNsense 23.7.3-amd64 if it works?

[franco]

Sure, here is the backport for 23.7.3:

https://github.com/opnsense/core/commit/f934046cb47

# opnsense-patch f934046cb47


Cheers,
Franco

[RamSense]

applied the patch

Code Select Expand

opnsense-patch f934046cb47
Fetched f934046cb47 via https://github.com/opnsense/core
Hmm...  Looks like a unified diff to me...
The text leading up to this was:
--------------------------
|From f934046cb478ceb8116721039c3d0ed17f62c5d2 Mon Sep 17 00:00:00 2001
|From: Franco Fichtner <franco@opnsense.org>
|Date: Fri, 8 Sep 2023 13:08:45 +0200
|Subject: [PATCH] interfaces: implement interface_configure_mtu()
|
|---
| src/etc/inc/interfaces.inc | 54 +++++++++++++++++++++-----------------
| 1 file changed, 30 insertions(+), 24 deletions(-)
|
|diff --git a/src/etc/inc/interfaces.inc b/src/etc/inc/interfaces.inc
|index 49c2d45fc3..7b4f637c54 100644
|--- a/src/etc/inc/interfaces.inc
|+++ b/src/etc/inc/interfaces.inc
--------------------------
Patching file etc/inc/interfaces.inc using Plan A...
Hunk #1 succeeded at 2172.
Hunk #2 succeeded at 2213.
Hunk #3 succeeded at 2221.
Hunk #4 succeeded at 2304.
Hunk #5 succeeded at 2373.
done
All patches have been applied successfully.  Have a nice day.

Did a reboot, and mtu is showing correct now at interfaces-overview MTU 1500! THNX!

[netnut]

Sure, here is the backport for 23.7.3:

https://github.com/opnsense/core/commit/f934046cb47

# opnsense-patch f934046cb47

Nice!

Applied the patch on 23.7.3 with pppoe on top of igb interface (Intel 350), works like a charm...

[furfix]

hello! Sorry for bringing up this topic again, but I've tried to set my PPPoE at 1500, but looks like no matter how I set my phisical interface + vlan, the pppoe is always created using 1492.

I'm using i225 nics and OPNsense 23.7.4-amd64, isp supports (mtu) 1500 bytes (rfc4638)

May I ask a little of help on how to applied the patch mentioned before?

https://github.com/opnsense/core/commit/f934046cb47

Thanks in advance!!
F

edit:
I sshed, and just push "opnsense-patch f934046cb47" and it worked :) Now pppoe is 1500. Thanks Franco!

[franco]

Ok wasn't fast enough.  8)

This will be included in 23.7.5 tomorrow.


Cheers,
Franco

[Taunt9930]

Ok wasn't fast enough.  8)

This will be included in 23.7.5 tomorrow.


Cheers,
Franco

Excellent, thanks.

Question - if we have previously enabled the parent igb interface just to set MTU to 1508 (and thus creating an annoying superfluous interface listing throughout firewalls etc.) can we now remove said interface in 23.7.5? If so, safest way of doing so?

Thanks, as ever, for your tireless efforts!

[franco]

The code will try to calculate the requirement for the parent and set it if it needs to be increased. If the parent is assigned it makes sure to look at the custom MTU value there and use that (even if it's too small).

The best course of action is to remove the parent assignment and let the function take are of it. This has the benefit of adapting to new situations automatically. If the parent can't be deleted for other reasons clearing the MTU value is the equivalent of deleting the parent from the scope of the MTU function.


Cheers,
Franco