IPv6 connections to GitHub (2606:50c0::/32) reset during TLS handshake – IPv4 fine – moderator help

nickfinch — Tue, 13 Oct 2026 15:56:52 GMT

Hi, I'd like a moderator to raise this with BT's network team please, as it's a routing issue rather than a line fault.

Problem: On BT Fibre (Smart Hub), HTTPS connections over IPv6 to GitHub's servers are reset by the remote end during the TLS handshake around 50–85% of the time. The same requests over IPv4 succeed 100% of the time. As a result, github.com pages load without their CSS/JavaScript and need several refreshes.

Affected: GitHub's IPv6 range 2606:50c0:8000::/48 to 2606:50c0:8003::/48 (hosts github.githubassets.com and avatars.githubusercontent.com). All four prefixes are affected.

Test results (13 Oct 2026, 15:50 UTC, wired Ethernet, no VPN/proxy/AV):
- IPv6 to github.githubassets.com: 17/20 failed ("Recv failure: Connection was reset" / "schannel: failed to receive handshake")
- IPv4 to the same host: 0/20 failed
- The TCP connection completes; the reset arrives during the TLS handshake
- It doesn't depend on the website name requested (same result with a different hostname to the same IP), so it isn't content filtering
- Not MTU: 1500-byte IPv6 pings (1452-byte payload) to the same address succeed with 0% loss
- Other IPv6 sites (Google, Cloudflare, Facebook) work 100% over IPv6

IPv6 traceroute:
1 <1 ms [my hub]
2 2 ms 2a00:2302::1103:203:66d
3 *
4 *
5 13 ms 2a00:2380:107::f9
6 *
7 13 ms 2606:50c0:8001::215

The route is short (BT → GitHub at about 13 ms), so this looks like a problem at or near the BT–GitHub connection point, possibly a faulty link or load-balancer member that only some connections hash onto.

Workaround in place: I've set Windows to prefer IPv4, but other devices in the house are still affected, and I understand IPv6 can no longer be turned off on the Smart Hub.

Happy to run further tests. Could this be passed to the team that handles BT's IPv6 connections to other networks?

Re: IPv6 connections to GitHub (2606:50c0::/32) reset during TLS handshake – IPv4 fine – moderator h

Crimliar — Tue, 13 Oct 2026 21:04:47 GMT

Excuse me for being stupid here but I though the handshake was end to end - ie between the server and client, which would be your end-point device and not the router? *Unless your device is masquerading (has it's uses)!

Using IPfoo as an extension in my browser, I see the main guthub accessed by IPv4, but various assets are accessed by IPv6 - I would have assumed this is normal!

Sorry if I'm off at a tangent, but I trying to understand the problem when all I really see is the internet being the internet!

This topic

IPv6 connections to GitHub (2606:50c0::/32) reset during TLS handshake – IPv4 fine – moderator help

Re: IPv6 connections to GitHub (2606:50c0::/32) reset during TLS handshake – IPv4 fine – moderator h