Netgate SG-1000 microFirewall

Author Topic: IPv6 with HE Tunnel: ping works, but TCP fails to establish  (Read 3956 times)

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Offline andrewknots

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Re: IPv6 with HE Tunnel: ping works, but TCP fails to establish
« Reply #15 on: September 24, 2016, 03:22:39 am »
My ISP decided they could supply IPv6 directly (Zen Internet) so I've now dropped the HE tunnel in favour of native support.  Sorry if that means I'm not helping others to resolve the issue, but for me it is a satisfactory outcome.

Thanks everyone for the help and support

Offline xurubin

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Re: IPv6 with HE Tunnel: ping works, but TCP fails to establish
« Reply #16 on: January 14, 2018, 03:38:43 am »
Some updates:

I recently switched to a new ISP (BT Infinity) so decided to give this another go. Unfortunately the exact same ACK dropping issue still happens with BT's Smart Hub (Home Hub 6A). This time I come across this post https://ttlexpired.co.uk/2016/02/12/ipv6-tunnel-and-failing-tcp-sessions/ describing a very similar issue from an engineer working for SKY and he concluded this is a bug with Broadcom SoC's "flow cache" mechanism, and by disabling flow cache the issue can be mitigated. Both my old SKY router SR102 and BT's new hub use Broadcom's SoC, so I have a strong suspicion that this is indeed the root cause.

I'm no longer with SKY so can't experiment with it, but for anyone stumbling across this post via Google, you might be able to play with it by compiling your own SR102 firmware from SKY's GPL tarball and try to disable flow cache. Unfortunately BT has yet to release the source code for its Smart Hub, so I'm still stuck.