[HowTo] - PPPoE, VLAN & RFC4638

[hushcoden]

QQ: My WAN interface has a 'parent' interface with an IP address on the same subnet of my modem, and I've created that interface to connect to the web gui of the modem.

I've now changed the WAN port MTU to 1508 -> the calculated MTU goes from 1492 to 1500 and the MTU of the parent interface shows 1508. So far so good, BUT I noticed in the interface statics that the parent interface has a never stop number of 'errors in' and 'collision': should I worry about or not?

Tia.

[netnut]

I've now changed the WAN port MTU to 1508 -> the calculated MTU goes from 1492 to 1500 and the MTU of the parent interface shows 1508. So far so good, BUT I noticed in the interface statics that the parent interface has a never stop number of 'errors in' and 'collision': should I worry about or not?

Yeah, you should.... But I would be surprised if this is related to this MTU change if your ISP is supporting RFC4638 and you're sure (double check) your NIC _supports_ >1500 MTU sizes. You can simply check by reverting the MTU change and see if these errors are still there in default (1492) mode.

Collision errors are in most cases related to duplex errors, check if your NIC speed & duplex settings are aligned with switch port or modem port. Auto Negotiation shouldn't be a problem for decades, but funky NIC's (Realtek) and cheap "smart" switches can still be trouble makers. You can try to set the speed & duplex settings fixed on _BOTH_ sides manually (10/100/1000Mb / Half/Full-Duplex), just be sure _BOTH_ sides are configured exactly the same (Fixed or Auto).

If you fix the collisions you probably fix the errors with it, but one step at a time .

[hushcoden]

Thanks netnut but indeed I started to see such errors just after I entered the MTU value 1508 on the WAN port - and just to be sure I was clear, those errors and collisions are on the parent interface and not on the WAN interface itself which luckily still shows no errors/collisions.

The NICs are I225-V and I'm pretty sure they support jumbo frames.

So, are you saying that this is a 'serious' issue even if it's on the parent interface of WAN?

P.S.
I tried to use VIP to accomplish the same result, but no luck at all, unfortunately, so this is for me the only way I can access the modem web GUI.

[netnut]

The NICs are I225-V and I'm pretty sure they support jumbo frames.

These go up to 9.5KB Jumbo's, so yeah, that NIC shouldn't be a problem. Are you really sure your ISP supports RFC4638 ? It's common, but certainly not default.

So, are you saying that this is a 'serious' issue even if it's on the parent interface of WAN?

Well, don't panic . But errors are BAD, no errors are GOOD .
Since the reboot for the v23.7.5 upgrade 19 days ago (and a non-reboot upgrade to v23.7.6) my pppoe and parents showing zero collisions/errors, that should be the norm...

Having collisions means something is sub optimal (or Realtek ), normally a collision gets resend so the effect is not always noticeable, especially on a single interface ISP uplink.

What does "Media" in  "INTERFACES: OVERVIEW" shows you at the physical parent interface ?

Other common things to check are the quality of your patch cable (try a non-self-made > CAT5e), and the connector (pull in/out and check if it fits firmly on both sides).

[hushcoden]

What does "Media" in  "INTERFACES: OVERVIEW" shows you at the physical parent interface ?

1000baseT <full-duplex>

Other common things to check are the quality of your patch cable (try a non-self-made > CAT5e), and the connector (pull in/out and check if it fits firmly on both sides).

Tested and it's all good.

Anyway, I changed the WAN interface MTU value back to 1492 and 'magically' no more errors in/collisions for the parent interface 

Also, in order for the parent interface to get back to MTU=1500 I had to restart OPNsense, but I recall in the previous versions that was happening 'on the fly'.

[netnut]

Anyway, I changed the WAN interface MTU value back to 1492 and 'magically' no more errors in/collisions for the parent interface

You still didn't confirm if your ISP is supporting RC4638, which is mandatory to make "this" work.

The only last suggestion I have, when your are using PPPOE on top of a VLAN, try to set the MTU on the physical parent interface to 1512. If that doesn't work I'm out of options...   

[hushcoden]

I did contact my ISP to confirm that, but no response so far. Besides, I had to replace my modem and the new one doesn't support MTU higher than 1500, so never mind I can live with 1492 

Many thanks !