I am running GNU/Linux version 3.4.113+ with a 6in4 tunnel to a tunnel broker. If I run command

ip -6 route list table local

I see a lot of routes. And one of this route entries is this

local ::1 via :: dev lo  proto none  metric 0  

This is the situation after a reboot of the server for several hours. Under certain circumstances this entry changes to this

local ::1 via :: dev lo  proto none  metric 0  rtt 18ms rttvar 15ms cwnd 10

Till now I couldn't figure out why. Are there any ideas what could cause this change ?

  • Those looks like they may be stats recorded by TCP in order to improve performance. But 18ms round trip time to localhost sounds like too much.
    – kasperd
    Feb 10 '18 at 14:31

After days of looking into logs and analyzing I found the reason. I am using a reverse SSH tunnel on this server. But this doesn't happen if the tunnel is opened. It happens if the tunnel is used actively the first time. As I am not always using this tunnel it took a while until I found the reason.

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