Weird behaviour with IPv6-gif-Tunnels since most recent update

Fri Nov 18 02:34:28 PST 2016

Hi,

Since our data centre provider does not yet provide native IPv6
connectivity, I have one of my servers act as IPv6 router by means of a
gif tunnel where IPv6 comes in (via SiXXS).

So far, so fine, worked like a charm.  I did an upgrade yesterday to get
the recently added LibreSSL-stuff.  Ever since, the tunnel behaves so
weird that it has become next to useless: There is packet loss at on
average 30%, which comes in bursts.  Packets seem to queue up, get
dropped at the end, after ten to thirty seconds, a slew of packets
gushes forth and comes in any order.  Lather, rinse, repeat, this
happens roughly every minute.

I had noticed practically the same behaviour a few months back on my
router at home (a Fritz!Box).  With IPv6 via Tunnel, I would get this
bursty, useless connection (it’s especially fun to work via SSH if only
seven out of ten characters make it through…)—with native IPv6 (which I
discovered then was available), the problem went away.

I can see the problem on both ends:  If I ping my router (or any server
behind it), traffic goes in bursts.  If my router pings the internet,
the output looks similar (except for pinging the remote end of the
tunnel, which goes without problems), but less often.

Right now, the machine is at 566cfef031.  I accidentally messed up my
notes, so I don’t exactly know where it was previously, but somewhere
shortly after 4.7 branch (most likely 50787d03cd0a)  The tunnel worked
fine ever since 4.4, the configuration has not been touched ever since
then, this behaviour is new.  It seems to be specific to it being a
-tunnel-; I have upgraded other servers to the same release before,
there were no hiccups when I talked to them via IPv6.

Here‘s what one of those burts looks ‚live‘:
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2153 hlim=54 time=33.826 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2154 hlim=54 time=33.492 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2155 hlim=54 time=32.558 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2156 hlim=54 time=33.827 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2157 hlim=54 time=32.249 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2158 hlim=54 time=34.037 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2159 hlim=54 time=32.766 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2160 hlim=54 time=32.389 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2161 hlim=54 time=32.409 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2162 hlim=54 time=33.587 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2163 hlim=54 time=33.818 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2164 hlim=54 time=32.405 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2165 hlim=54 time=32.170 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2166 hlim=54 time=32.236 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2167 hlim=54 time=32.564 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2168 hlim=54 time=32.849 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2169 hlim=54 time=32.228 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2170 hlim=54 time=34.583 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2171 hlim=54 time=32.989 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2172 hlim=54 time=34.260 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2173 hlim=54 time=32.385 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2223 hlim=54 time=34.144 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2224 hlim=54 time=33.777 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2225 hlim=54 time=32.364 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2226 hlim=54 time=33.040 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2181 hlim=54 time=46208.753 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2182 hlim=54 time=45784.141 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2183 hlim=54 time=45034.544 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2227 hlim=54 time=37.508 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2184 hlim=54 time=44527.394 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2228 hlim=54 time=33.404 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2185 hlim=54 time=44639.041 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2229 hlim=54 time=33.999 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2186 hlim=54 time=44087.804 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2187 hlim=54 time=43310.014 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2188 hlim=54 time=42649.367 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2189 hlim=54 time=41888.085 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2230 hlim=54 time=34.552 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2190 hlim=54 time=41082.922 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2192 hlim=54 time=39293.069 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2193 hlim=54 time=38280.420 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2194 hlim=54 time=37276.122 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2195 hlim=54 time=36242.645 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2196 hlim=54 time=35247.982 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2197 hlim=54 time=34250.600 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2231 hlim=54 time=33.996 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2232 hlim=54 time=32.236 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2233 hlim=54 time=33.578 ms                    
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2221 hlim=54 time=13131.371 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2222 hlim=54 time=12136.902 ms                 
| 16 bytes from 2a01:1e8:e100:874c:1:72ff:fe6b:e33e, icmp_seq=2234 hlim=54 time=32.255 ms                 

Any help is greatly appreciated,

    Stefan

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