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It appears EE are not sending back Type 2 messages on ICMPv6 when a packet is too large.
This breaks pmtu discovery, with the result that some ipv6 sites work (ie cloudflare seems fine), others don’t (amazon, icloud) - presumably depending on the specific routing in place in BTs network
I’ve found the only safe option is to back right off to 1280 mtu (1220 nah) since there’s no knowing when a packet may arrive at a router too big.
Secondly, fragmented ipv6 packets are also blocked - though this is more common these days.
The impact of both is black holes. In my case with cloud/backup
Anyone else seen this? reported this?
How are other ISPs for this?
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planetf1
