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Author Topic: IPv6 seems ok: ping ok, but TCP fails  (Read 1230 times)

Celotoise

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  • Posts: 3
IPv6 seems ok: ping ok, but TCP fails
« on: July 29, 2019, 10:51:50 PM »
Hi,

I'm using a draytek 2925.

The he tunnel ipv6 seems ok : ping both ways are working.

But web TCP sessions fails.

Any help for fix or troubleshooting  is welcome.
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cholzhauer

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Re: IPv6 seems ok: ping ok, but TCP fails
« Reply #1 on: July 30, 2019, 04:53:29 AM »
Sounds like an MTU mismatch
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Celotoise

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  • Posts: 3
Re: IPv6 seems ok: ping ok, but TCP fails
« Reply #2 on: July 31, 2019, 11:13:05 AM »
tested multiple IPV6 MTU (1300,1442,1472..) on the windows 10  : no success

Any possibility to monitor or some stat on the traffic from HE point a view ?
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Celotoise

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Re: IPv6 seems ok: ping ok, but TLS fails
« Reply #3 on: August 01, 2019, 12:05:27 AM »
More info:

from google chrome: http ok but when switching to https timeout during the tls session

Current MTU on HE is 1460
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alerinaldi

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  • Posts: 3
Re: IPv6 seems ok: ping ok, but TCP fails
« Reply #4 on: October 14, 2019, 03:34:22 AM »
Hello,
this is a thing that made me struggling for many hours. Finally, I discovered this is a quite well-known Broadcom chipset issue:

https://ttlexpired.co.uk/2016/02/12/ipv6-tunnel-and-failing-tcp-sessions/

If you have full control of your router, you can issue those commands to disable flow cache:

fcctl disable
fcctl config --mcast 0

Maybe your router has some GUI options to toggle those settings, too.
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tullygray

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  • Posts: 1
Re: IPv6 seems ok: ping ok, but TCP fails
« Reply #5 on: March 30, 2020, 12:24:40 PM »
Thanks alerinaldi, this works for me.
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