I'd love to hear if anyone can validate this -- I've been fighting with an iOS power drain issue, but in fact it's actually a IPv6 issue which occurs both with the EE Homehub AND with a opnsense router. Basically it seems as if the EE network is breaking path mtu discovery both by dropping fragments, and in not returning the correct ICMP responses.
This is quite technical but it's quite a fundamental issue (it feels to me as it's a 'broken network'). Of course I may have made an error:
More complete AI-summarised version below.
Observation: The upstream network (EE/Openreach backhaul) appears to silently discard outbound IPv6 packets that require fragmentation. This breaks Path MTU Discovery (PMTUD), causing connectivity stalls and high battery drain on devices attempting to negotiate packet sizes (e.g., Apple devices using iCloud Private Relay).
Context: ISP/Plan: EE Full Fibre 900/110. Hardware: Tested on EE Smart Hub Plus and confirmed consistent on OPNsense (Intel N100). MTU: Link negotiates at 1492 bytes (PPPoE standard).
The Limitation: The network accepts unfragmented packets up to the link limit (1492 bytes) but drops any packet that is fragmented, regardless of total size. Crucially, it fails to send back ICMPv6 Type 2 (Packet Too Big) or Type 3 (Time Exceeded), creating a silent "black hole."
Test Methodology (Reproducible)
You can replicate this on any Linux/macOS device (Pi, Mac, etc.) connected to the router. You need two terminal windows open.
Step 1: The Monitor (Terminal A) Run this to listen for "Packet Too Big" or error messages from the ISP.
sudo tcpdump -n -i any "icmp6 && (icmp6[0] == 1 || icmp6[0] == 2 || icmp6[0] == 3)"
Step 2: The Trigger (Terminal B) Run these pings to test the boundary.
Test A (Standard Packet - 1492 bytes): Payload 1444 + 48 bytes headers = 1492 bytes (Fits in one frame)
ping6 -c 3 -s 1444 ipv6.google.com
Result: Success.
Test B (Fragmented Packet - 1493 bytes): Payload 1445 + 48 bytes headers = 1493 bytes (Forces fragmentation)
ping6 -c 3 -s 1445 ipv6.google.com
Result: 100% Packet Loss.
Step 3: Verification Look at Terminal A. Expected Behavior (RFC Compliant): You should see an ICMPv6 error message. Actual Behavior (Black Hole): The terminal remains completely blank. The packets are dropped silently.
