Re: limiting SSH client's bandwidth?



On Thu, 2009-02-12 at 12:40 +0100, Tomasz Chmielewski wrote:
Is it somehow possible to limit OpenSSH client's bandwidth?

Today I was copying data (whole block devices) over internet
with:

dd if=/dev/san10/xen1 | bzip2 -9 | ssh 192.168.15.46 "bzip2 -d | dd of=/dev/san18/xen1"


It worked fine, but the latency of other connections was horrible,
because the above connection ate almost all bandwidth available.


scp has this option:

-l limit
Limits the used bandwidth, specified in Kbit/s.

But it looks that it's not available to ssh.

I wouldn't like to use 3rd party programs or system settings,
because they are not portable, sometimes require root privileges
and are just additional burden for a one-off task.



SSH has always been meant for interactive shell - not file copying.
therefore, the -l (or similar) flag has no point there (unless your are
piping file copy operations through SSH) :D

Other problem is that SSH (being meant for interactive shell) sets the
TOS (type of service) bits to 'minimize delay'. SCP on contrary does not
do this, so even not throttled scp (full bandwidth) won't spoil your
concurrent ssh interactivity, because default qdisc attached to each
device on linux - pfifo_fast honours TOS bits - will send out SSH
traffic first, let the scp traffic queue.

M.



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