Help debugging pfSense modem intermittently dropping connection with Mercury ISP

Forums › LAN (ethernet/Wifi/routers/Bluetooth) › Help debugging pfSense modem intermittently dropping connection with Mercury ISP

crashy

3 posts

Wannabe Geek
+1 received by user: 1

#319857 9-Jun-2025 08:28

I have been able to setup my pfSense box to work with Mercury ISP using the following Geek Zone post: https://www.geekzone.co.nz/forums.asp?forumid=49&topicid=314975

What I am having trouble with is every now and then my WAN will loose connection, I want to say it's to do with being issued a new public IP on the ISP side but I'm not entirely sure that's correct.

I have distilled the process for restoring my WAN down to the following steps:

1. Unplug all of the ethernet ports except
a. ONT to modem
2. Boot into pfSense console (on the actual pfSense box)
3. Select Reset to factory defaults (4)
4. Select Assign interfaces (1) and
a. LAN to em0
b. WAN to em7 (this will have an empty IP initially)
5. Select reboot (5)
6. Plug ethernet cables back in
a. Modem to switch
b. Switch to Laptop/Desktop
7. Check that the auto assigned IP on Laptop/Desktop is `192.168.1.XXX`
8. Go to https://192.168.1.1/
9. Accept defaults for Wizard
10. Go to https://192.168.1.1/interfaces_vlan.php
a. Set **Parent Interface** to `em7 (00...`
b. Set **VLAN Tag** to `10`
c. Set **Description** to `Mercury`
11. Go to https://192.168.1.1/interfaces_assign.php
a. In the dropdown next to **WAN** select `VLAN 10...`
12. Go to https://192.168.1.1/interfaces.php?if=wan
a. Set **IPv4 Configuration Type** to `DCHP`
b. Set **IPv6 Configuration Type** to `None`
13. Reboot modem
14. Plug in remaining ethernet ports

Obviously this is somewhat cumbersome and I'd like to get to the bottom of why the WAN periodically drops (at the moment the frequency is probably ~1 per month).

I inherited my kit from a sysadmin at work and while I have some technical knowledge networking is not my strong suite but something I want to improve at.

What would be the correct way to start debugging this issue so I can isolate the root cause?

Additional notes:
- Unplugging the ethernet ports from the switch seemed to stop devices being auto assigned IP address that were not in the 192.168.1.XXX range
- Manually setting an assigned IP with DHCP + manual address did not seem to work (I couldn't ping the pfSense box)

shk292

2916 posts

Uber Geek
+1 received by user: 2040

Lifetime subscriber

#3382016 9-Jun-2025 11:28

IMHO if you’re not sure about the difference between a router and a modern, you’d be better off using a consumer router than fiddling around with pfsense.

crashy

3 posts

Wannabe Geek
+1 received by user: 1

#3382017 9-Jun-2025 11:34

That's totally fair feedback, that being said I'm trying to improve my understanding of networking and part of the process is fiddling and learning these things along the way.

muppet

2642 posts

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#3382078 9-Jun-2025 12:17

Are you 100% sure you don't have more than one device on your WAN interface that's requesting a DHCP lease? (Oh if it's only happening once a month, probably not)

What's your Modem in this context?

When it "drops" does it still think it has a DHCP lease? Have you set it to keep requesting/renewing a DHCP lease should the current one expire (BNG ugprades/LFC upgrades etc)

Once it's dropped how do you fix it, reboot? Can you just manually request a new DHCP lease, does that work?

mentalinc

3384 posts

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#3382081 9-Jun-2025 12:35

Agree, very confusing if there is a "modem" and Pfsense in the mix.

Also 14 steps seems too extreme.

enable and disable the WAN interface in PFsense should be enough to bring it all back to life.

Can you do a basic diagram?

e.g.: ONT -> Modem -> PFsense .... or ONT -> PFsense ....

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crashy

3 posts

Wannabe Geek
+1 received by user: 1

#3382083 9-Jun-2025 12:43

Sorry I can see I have used the word modem incorrectly, I think the word I should have was router. In terms of what the setup looks like it is:

ONT -> pfSense box -> Cisco ethernet switch -> Household computers / Unifi AP

> Are you 100% sure you don't have more than one device on your WAN interface that's requesting a DHCP lease?

No I'm not, it is worth noting that at about the time it went offline I had just plugged in a new ethernet cable to another desktop, shortly after that the WAN stopped working in the sense that I could still connect to the WiFi but had no internet access. Initially I chalked it up to bad timing because I had plugged cables in/out between now and the last time it had gone offline but it is possibly related.

> Have you set it to keep requesting/renewing a DHCP lease should the current one expire

This could be it, I will look into this this evening and see if this is related.

Thanks everyone for the help so far, will post back with what I find. Can appreciate that I need to improve my understanding of all of the above.

muppet

2642 posts

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#3382103 9-Jun-2025 13:16

crashy:

Can appreciate that I need to improve my understanding of all of the above.

There's only one really good way to learn, and you're doing it!

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nitro

757 posts

Ultimate Geek
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#3382110 9-Jun-2025 13:37

how/why do you suspect it's your DHCP link to your provider that's causing grief? have you seen your WAN IP address change? if this were the case, disabling the pfSense router WAN port or disconnecting the ethernet cable between ONT and pfSense router (and reconnecting!) should get you a new ip address and restore your connection. no need for your multi-step restoration regime.

leads me to think there could be something else... what does pfSense say? have you checked the logs?

good luck on your journey with networking, but it may also help to have another router (perhaps from your provider) that is simply plug-n-play. this would help you isolate the issue between your provider and your pfSense router (maybe something in your config, perhaps). the Cisco switch can also be configured many different ways.