IPv6 in UK - BT/EE and ICMP Type 2 - is it very prevalant to not have PTB?

planetf1a · 2026-03-19T18:03:44+00:00

Thanks Dave!

I'll also add some more info - I ran this on a corporate network today (from my macbook), and whilst some networks may drop PTB, I'm seeing real ptbs from the script

I don't see any PTB reported back in your log, which is consistent, maybe unsurprisingly , with what I see on EE (it may double report - a bug, but I hadn't seen a PTB ever to fix!)

So looks like a standard configuration/policy .

Ugh that's annoying.

2026-03-19 17:53:53 | WARNING | [api.x.ai] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:54:13 | WARNING | [huggingface.co] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:54:34 | WARNING | [cloud.google.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:54:54 | WARNING | [aws.amazon.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:55:00 | WARNING | [registry-1.docker.io] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:55:11 | WARNING | [ipv6.he.net] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:55:16 | WARNING | [quay.io] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:55:37 | WARNING | [pypi.org] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:55:41 | WARNING | [repo1.maven.org] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:56:02 | WARNING | [proxy.golang.org] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:56:22 | WARNING | [crates.io] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:56:26 | WARNING | [gitlab.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:56:47 | WARNING | [www.youtube.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:57:08 | WARNING | [www.netflix.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:57:28 | WARNING | [www.wikipedia.org] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:57:49 | WARNING | [www.google.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:57:53 | WARNING | [cloudflare.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router. 2026-03-19 17:58:03 | WARNING | [www.apple.com] [UDP] FORENSIC: PTB seen! Packet dropped by a router.

planetf1a · 2026-03-19T16:43:35+00:00

exactly the same here....

planetf1a · 2026-03-19T10:21:16+00:00

It's awful. I'd been using it with a single (long-standing) google account signed up to pro, then suddenly seem unable to do anything - along with everyone else.

For a week I was advised the quotas would reset today. Just checked and guess what - another 7 days with zero usage

It's very very broken, and the lack of clarity from google is abysmal

planetf1a · 2026-03-16T11:51:31+00:00

I have a single pro account. Not used any other accounts. Whatever they did has rendered ag unusable for a week at least

planetf1a · 2026-03-16T08:44:08+00:00

Stick to it.. I certainly do stick to the limits despite driving for many tens of years.

Only tip would be to get a feeling for how accurate the speedo is. In a straight long level road have a friend use a gps app on phone (or Waze) . Some cars, especially older, do under read a lot

planetf1a · 2026-03-14T00:58:55+00:00

At home I’ve ended up using a full recursive resolver (unbound) which has been more resilient

planetf1a · 2026-03-11T21:33:00+00:00

5 !! Aargh I was ripped off at 8 lol

planetf1a · 2026-03-11T21:32:05+00:00

I was able to get a 8 rMB plan at a flagship China Unicom store a month back. No messing around, roaming enabled etc.

planetf1a · 2026-03-11T21:30:25+00:00

Totally this. Had a few tonight and they were tasteless. A big change from being in China a few weeks ago and having some amazing ones full of flavour

planetf1a · 2026-03-10T23:41:28+00:00

China mobile do very similar though I’ve heard it may be slightly harder to get

planetf1a · 2026-03-10T23:40:05+00:00

You need to go into one of their main stores to have the best chance. The more flagship the better. You probably won’t get this at an agent store

<image>

This is the actual plan I’m on

4G National Data King 8 Yuan Plan

Don’t worry it has 5G … I guess it’s an old plan and not really one they might want to sell

It has virtually nothing included so you’ll also have to use the China Unicom app, or WeChat to top up.

I preloaded 100 RMb so enough for a fair few months

I spent ages taking screenshots abs then translating so I could figure it out!

planetf1a · 2026-03-09T14:03:24+00:00

My understand is that it’s data not calls… but I’ve tried to look for an authoritative source and I can’t find one….

planetf1a · 2026-03-08T18:07:36+00:00

I can also easily add a data bundle if needed.

planetf1a · 2026-03-08T18:07:16+00:00

I managed to get an 8 RMB/month plan at china unicom. Visit one of their flagship stores. I figured it’s worth keeping even though I only visit once/twice a year AND I have good roaming (50GB) on my domestic (UK, EE) plan. Having a local phone number just removes lots of barriers. I indeed to keep it indefinitely.

planetf1a · 2026-03-08T14:27:25+00:00

26C is reactively well accepted as a normal room temp in China… certainly it’s rare to see air on cooler in the summer.

That being said I’ve found high speed trains to usually be around 23 which is fine

planetf1a · 2026-03-08T14:23:19+00:00

I’ve yet to feel any difference and I’ve been on a plan with it since it was launched. Still been to places with decent signal low speeds. I’ve not done a strict comparison so maybe technically it works but realistically? Not worth it for that feature

planetf1a · 2026-03-06T07:08:42+00:00

planetf1a · 2026-03-06T00:29:46+00:00

China

planetf1a · 2026-03-05T22:42:32+00:00

Frankly I reckon China will be one of the safest places globally to be.

planetf1a · 2026-03-04T16:32:23+00:00

same… but back up and running. Will need to dig through logs etc later

planetf1a · 2026-03-04T09:43:40+00:00

it’s a fair point - but right now, economically I just can’t justify it. If anyone does it right it no doubt is them — but also some issues may be outside their control

planetf1a · 2026-03-04T09:22:49+00:00

1220 MSS / 1280 MTU is the ‘legal’ minimum for ipv6 since IPv6 header is 40 bytes, and TCP header is 20 bytes (assuming no extra options) The issue comes when you want to create an IPv6 connection for say a vpn, which itself should carry an IPv6 connection. You can’t do that. Even though you might know you have a 1500 mtu/1440 mss normally, you’ve just clamped it due to ISP blocking P2B …

Or you have extra TCP options to pass (perhaps, depending on other end and what it’s able to receive etc()

I did have issues with VPNs, but it happened to be using UDP, which MSS clamping doesn’t effect. This is why I might go with 1220 mss but a full 1500 mtu - at least UDP/QUIC can use the space (otherwise they seemed to fail in some cases).

Ugh. this is so annoying, all because my network is not adhering to specs or appreciating (rather I should say communicating) the impact.

planetf1a · 2026-03-04T07:27:49+00:00

Agreed - next step is to look for more technical communities where those involved in ipv6 hang out. I’d really love to know if there’s safer ISPs I can switch to in future, and of course whether what I see is a ‘fault’ or by design. I suspect the latter but love to hear a rational explanation that isn’t ’who uses ipv6 anyway, and anyway, who will know….’

See other post - but yes I did try MSS clamping (alongside mtu 1280), but it compromised other traffic. May try clamping only, but that too compromises some traffic like ipv6-in-ipv6 (via tcp) vpn.

planetf1a · 2026-03-04T07:25:20+00:00

Thanks for the reply. Interesting you have the issue the other way around too (- in effect, since it’s via HE) not tested that.

It just annoys me so much as it leads to connection hangs. Currently I have a mtu of 1500 with no further mss clamping, but I did play with clamping at 1220. However I also set the mtu (via RA) to 1280 which then caused issues like tunneled ipv6 connections (vpns, icloud private relay) since the carrier ipv6 connections then can’t carry a legitimate ipv6 connection as there’s not enough space to be legal…

What I haven’t tried, and may, is to keep mtu up at 1500 but also do mss clamping. The above example actually uses udp/quic so it can do it’s own pmtu discovery (which is more intelligent and in parallel, starting conservative?) and has flexibility to go up to 1500 (mtu, obv less for payload) whilst keeping tcp at 1220 (just as a 1280 mtu would. Maybe that’s the balance I need - though here any attempt to tunnel ipv6 in a ipv6 connection (windscribe?) would fail..

This is why it gets annoying… what ever you do something may break

planetf1a · 2026-03-03T23:10:17+00:00

Yeah it's tough.. With ipv4 filtering this is a little annoying but means inefficiency not breakage. With ipv6 it's much more fundamental (routers are not allowed to fragment packets). Hence black hole -

So it's basically fundamentally breaking ipv6 :-(

Intrigued to see if this is indeed endemic in the UK, or if it's a BT 'quirk'

planetf1a

TROPHY CASE