Bug 1115075 – All IPv6 transfers (rsync, scp, ftp) are running very slow, IPv4 is 40 times faster via IPv4 than IPv6

Bug 1115075 - All IPv6 transfers (rsync, scp, ftp) are running very slow, IPv4 is 40 times faster via IPv4 than IPv6


Summary:	All IPv6 transfers (rsync, scp, ftp) are running very slow, IPv4 is 40 times ...

Status:	RESOLVED INVALID

Classification:	openSUSE
Product:	openSUSE Distribution
Classification:	openSUSE
Component:	Network
Version:	Leap 15.0
Hardware:	Other Other

Priority:	P5 - None Severity: Normal (vote)
Target Milestone:	---
Assigned To:	E-mail List
QA Contact:	E-mail List

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Reported:	2018-11-07 16:41 UTC by Michael from Offenbach Germany
Modified:	2018-11-07 23:12 UTC (History)
CC List:	0 users

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Description Michael from Offenbach Germany 2018-11-07 16:41:27 UTC

VPS, Leap 15.0
box @home, also Leap 15.0
both with latest patches.

Very often, but not always, encrypted transfers from my VPS to my Leap 15 box at home, are running awfully slow when connected from client to server via IPv6. 

Same transfers via IPv4 runs always fast, >40 times faster than via IPv6.

Tested with netcat and speedtest, pure TCP:
VPS's network bandwith is nearly the promised 100MBit/sec
box@home's network bandwith is also nearly as promised, 50MBit/sec download, 10Mbit/sec upload (VDSL)
Measured netcat speed was 5-6 MB/sec

Having general network issues sorted out, I was at first thinking that maybe VPS's shared CPU power might be not over-stressed because of encryption, BUT:

When running several e.g. scp sessions in parallel, test with different large files, all of them are running at the same (slow) transfer speed of 100 +/- MB/sec. Up to the IPv4-for-1-session maximum of ~ 5MB/sec.

Any hints how to narrow down this strange issue?

Comment 1 Michael from Offenbach Germany 2018-11-07 20:36:42 UTC

Asked about this in mailing list openssh-unix-dev (openssh-unix-dev@mindrot.org)

Got the advice to test with a different protocol. Tested both with HTTPS (download from my Nextcloud instance) and FTP (set up pure-ftpd).

Result: FAST with IPv4, SLOW with IPv6

So seems to be a encryption and protocol independent IPv6 issue.

Comment 2 Michael from Offenbach Germany 2018-11-07 23:12:44 UTC

Found something new: My (Leap 15.0) VPS hosting company (now) offers an additional "rescue system", Debian 9 "Live". Started, configured IPv6, tried once more.

Result: Same factor 40 IPv4 vs IPv6 speed difference than with running Leap 15.0 on my VPS.

As my box@home is Leap 15.0, I wanted to be sure now that this issue is NOT related to Leap 15. So I've tried via FTP to download from the Debian Live system to my Android smartphone. SAME result, IPv4 MUCH faster.