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It seems like sometimes there are some connectivity problems around the edge of our network to certain other networks, and my ssh sessions with some remote servers, which themselves have no connectivity issues, drop.

Remotely, the sessions still appear as active; locally, I have optimised Windows 7 TCP for PuTTY to not drop connections on brief outages (with anything below 7 minutes being brief, and our edge connectivity issues probably last at most around 1 or 2 minutes), so, I'm thinking there's probably some reply packet that some edge equipment generates for my ssh client to keep dropping the connection during such otherwise-unnoticeable and very brief connectivity issues. RST, maybe? There's no NAT. This issue happens most often over IPv6 (that's what I mostly use), but I think IPv4 may also affected (did my TcpMaxDataRetransmissions fix not apply to IPv6?); the whole network is GigE and above.

What's the packet?

Would it be safe to ignore it? (for ssh)

Unless there's a simple OS setting for this, I plan on ignoring it with pf(4) around my network segment.

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cnst
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It seems like the TcpMaxDataRetransmissions from HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip\Parameters may indeed not apply to IPv6, even though Microsoft claims that's what has to be changed for the TCP stack, without any IPv4 / IPv6 mention!

In fact, there's already a separate HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\TCPIP6\Parameters in my X230 (they can't even keep the case consistent); I've added TcpMaxDataRetransmissions with a value of 0x18 to it; I expect that it'll likely resolve the issue (alas, only after a reboot).

cnst
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  • So, I did this, rebooted, and it doesn't seem to help. Still the IPv6 connection gets aborted for no obvious reason; just happened again right now: the last output in the terminal was a timestamp of 20:08; connection is marked as aborted by PuTTY at 20:08:11 (clocks should be in sync), saying, `2013-12-10 20:08:11 Network error: Software caused connection abort`. – cnst Dec 11 '13 at 04:13
  • This definitely doesn't work. It would appear that a few packets are lost, and the connection almost immediately terminates, only with IPv6. – cnst Jan 15 '14 at 22:11
  • Related: http://superuser.com/questions/702275/windows-7-putty-drop-ipv6-tcp-connections-on-brief-outages – cnst Jan 15 '14 at 22:48