Anyone noticed v4 traffic not working on 2Degrees?

Forums › 2degrees (including Slingshot, Orcon, Flip, Stuff Fibre, MyRepublic, 2talk and Vocus) › Anyone noticed v4 traffic not working on 2Degrees?

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Master Geek
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#323721 6-Jan-2026 10:15

Woke up this morning and found that HTTP(S) traffic on my 2Deg connection is no-longer working via IPv4 but v6 traffic is fine.

I am able to ping v4 addresses and resolve hostnames against v4 DNS server as well. Occasionally I'm able to bind a socket over HTTP/HTTPS to a remote web server but generally it fails (never get a SYN-ACK back)

No idea what would cause this strange behavior - no changes to router config on my end, just stopped working suddenly...

Anyone else noticing something similar?

Pat

Twitter: squip88

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#3450293 6-Jan-2026 10:20

Any troubleshooting done? Restarted router and switches?

Tried different DNS?

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67 posts

Master Geek
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#3450297 6-Jan-2026 10:23

Yeah I should have said that - rebooted everything. I did try alternative DNS prior to noticing that it was v4 specifically.

Such an odd one :(

Pat

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#3450310 6-Jan-2026 11:00

No problem here in Wellington. I have IPv6 turned off on one computer because it caused a problem, can't remember what, so it's IPv4 only and working fine.

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#3450313 6-Jan-2026 11:02

@ping No problem on 2degrees fibre at home

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67 posts

Master Geek
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#3450314 6-Jan-2026 11:02

Thanks; just wanted to check :) Im also in WLG so it must be me specifically.

Cheers

Pat

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boosacnoodle

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#3450321 6-Jan-2026 11:34

Working fine for me with 2d on V4. What router are you using?

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67 posts

Master Geek
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#3450324 6-Jan-2026 11:37

Mikrotik RB5009UG+

Pat

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nzkc

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#3450374 6-Jan-2026 14:47

I have the same router, am on 2d too but in Auckland. All fine for me.

Sounds suspiciously firewall related. Changed any recently?

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67 posts

Master Geek
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#3450376 6-Jan-2026 14:51

Nah nothing had changed for the longest time; I figured it was some weird CGNAT thing.

I raised a case with 2degrees; they said they changed something and now im working again - I wish I inquired to what they did but I cant be bothered trying to get through to tech support again.

Pat

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michaelmurfy

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#3450382 6-Jan-2026 15:08

Hmm I’ve seen this with somebody else recently in Wellington and support didn’t know what it was. We tried multiple routers, got a CG-NAT V4 address but it appeared no return route past their BNG - a Static IP appeared to fix it. Needed to get them online and they didn't require a static IP so in the end was basically forced to churn to another ISP (Quic) to get them running properly. I know all providers have issues but this individual wasn’t keen on paying for something they wouldn’t otherwise need to fix it.

There has been some other odd issues posted on here caused by CG-NAT that moving to a Static / Public IP or another ISP fixes.

This makes no sense as to why a Mikrotik is having issues. At first I thought it was just a weird quirk with some routers (in this case a Spark Smart Modem 3) but after my recent example and now this I’m thinking this isn’t the case.

Edit: To clarify - same issue as the OP where we could sometimes get out, but couldn't get back in with mainly UDP traffic so sounds like CG-NAT port exhaustion.

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67 posts

Master Geek
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#3450463 6-Jan-2026 21:08

michaelmurfy:

Hmm I’ve seen this with somebody else recently in Wellington and support didn’t know what it was. We tried multiple routers, got a CG-NAT V4 address but it appeared no return route past their BNG - a Static IP appeared to fix it. Needed to get them online and they didn't require a static IP so in the end was basically forced to churn to another ISP (Quic) to get them running properly. I know all providers have issues but this individual wasn’t keen on paying for something they wouldn’t otherwise need to fix it.

There has been some other odd issues posted on here caused by CG-NAT that moving to a Static / Public IP or another ISP fixes.

This makes no sense as to why a Mikrotik is having issues. At first I thought it was just a weird quirk with some routers (in this case a Spark Smart Modem 3) but after my recent example and now this I’m thinking this isn’t the case.

Edit: To clarify - same issue as the OP where we could sometimes get out, but couldn't get back in with mainly UDP traffic so sounds like CG-NAT port exhaustion.

Thanks for that info - that's super interesting. The edit you made to your last message also sounds pretty logical.

Its regressed tonight and internet usage is super frustrating; Guess I'll have to try navigate through their tech-support hell again :|

Pat

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#3450477 7-Jan-2026 00:00

@ping or you can tag a 2degrees staff member in this thread

michaelmurfy

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#3450479 7-Jan-2026 00:27

Ping: Its regressed tonight and internet usage is super frustrating; Guess I'll have to try navigate through their tech-support hell again :|

The problem was finding anyone who knew what I was talking about - hence the churn to an ISP that doesn't use CG-NAT and was around the same price. But I do think it is CG-NAT Port Exhaustion.

Having a full public IP address beats CG-NAT anytime. Especially for those running services.

Linux: @ping or you can tag a 2degrees staff member in this thread

Remember this isn't official support. Sure there are 2degrees staff here but pinging them for every problem isn't ideal especially when this has happened quite a number of times now (from a quick search):

https://www.geekzone.co.nz/forums.asp?forumid=81&topicid=317547&page_no=1#3302235

https://www.geekzone.co.nz/forums.asp?forumid=66&topicid=312833&page_no=2#3233704

https://www.geekzone.co.nz/forums.asp?forumid=49&topicid=320401

It's more of a problem if you're running torrent software or anything that uses a tonne of ports - which my example was.

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67 posts

Master Geek
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#3450486 7-Jan-2026 08:19

Yeah I'll try the official route (I dont lurk here enough to know anyone at 2D anyway :P )

CG-NAT was one of those things 2D thrust upon us around the time Vocus took over I think. I'm not running torrents I'm just trying to do my job during the day which unfortunately requires interacting with many v4 endpoints.

If I cannot make traction today I'll probably end up using your referral code to Quic - they look like they're pretty onto it.

Pat

Twitter: squip88

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67 posts

Master Geek
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#3450582 7-Jan-2026 15:53

Incase anyone runs into this; I think @michaelmurfy was correct - got a static IP set and can no longer reproduce the problem

Pat

Twitter: squip88

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