openssh-based file transfers (e.g. rsync, scp, ...) are running 40 (!!) times faster via IPv4 than IPv6

[michaelof at rocketmail.com]

Servus Philipp,


Unfortunately the traceroute(6) results are both more or less random. Sometimes traceroute "hangs" a while, wherever,
sometimes traceroute6. Sometimes traceroute is faster, sometimes traceroute6. Not reliable.

Your MTU question, tried as adviced:

Maximum size for IPv4 is 1466, and max size for IPv6 is 1444. Exceeding these values leads to a "ping: local error:
Message too long, mtu=1492" in both cases.

My Fritzbox says "Native IPv6", no tunnel, no underlying "IPv4 via DS-Lite". These are the default settings for ISP
"Deutsche Telekom", VDSL-50.


VINCENZO: Tried as adviced to test with FTP, installed pure-ftpd and opened VPS's ftp port in firewall. Maximum IPv4
speed was much slower (1.5-2 MB/sec) than other tests, maybe temporary issue or virtualization. But again: IPv6 was MUCH
slower than IPv4.





Am 07.11.18 um 20:57 schrieb Philipp Marek:
> 
>> first post to list, hopefully on-topic. Haven't found anything on the
>> net, tried to ask at first in OpenSuse forums a
>> while ago
>> (https://forums.opensuse.org/showthread.php/533588-rsnapshot-rsync-massive-performance-decrease)
>> and today
>> opened a bug in OpenSuse's Bugzilla
>> (https://bugzilla.opensuse.org/show_bug.cgi?id=1115075)
>>
>> As written in bug report, as general network issues could be excluded,
>> any hints where to start, how to narrow down if
>> this is a specific openssh issue or something else?
> 
> Your IPv6 _route_ has 3 times the latency:
> 
>   $ time /usr/sbin/traceroute vserver.domain.tld
>   ...
>    7  domain.tld (IPv4)  26.002 ms !X  24.859 ms !X  25.230 ms !X
> 
>   $ time /usr/sbin/traceroute6 vserver.domain.tld
>   ...
>    8  domain.tld (IPv6)  80.430 ms !X  79.301 ms !X  80.444 ms !X
> 
> The big time waster seems to be this link:
>    6  nug-d-i40-v6.telia.net (2001:2000:3018:8d::1)  32.046 ms  23.850 ms  24.097 ms
>    7  contabo-ic-305268-ffm-b11.c.telia.net (2001:2000:3080:953::2)  74.829 ms  77.704 ms  78.066 ms
> 
> I'll now speculate that you might as well have some MTU mismatches,
> meaning that packages have to get split up along the way, further
> slowing down your connection.
> 
> Do you have native IPv6 all the way, or is there an 6-in-4 tunnel
> inbetween (from the fritzbox on)?
> 
> Please try
>    # ping -M do -s <size> <ip>
> for sizes between 1300 and 1500 and find the largest (even) packet size
> that still works, and then do the same with ping6 as well.
> 
> Also note whether some packetsize works, but just larger ones vanish
> along the way.