Hi Saku,
On Thu, 13 Feb 2014, Saku Ytti wrote:
OpenSSH is conforming to this "informal standard", and with its huge
installed user base, helping to define it as well. It already does set
a high-priority TOS flag on interactive sessions, and low-priority on
non-interactive ones:
I've never ever seen DSCP 0x4 used for anything.
That's because it's not a DSCP at all. It would be 000001 in the
"Experimental or Local Use" block, and it has no standardised meaning
in DSCP at the moment.
What it is, is TOS 0x4 or "High Reliability" (which I take to mean as "we
want this packet delivered, no matter how late).
But OpenSSH apparently doesn't use it. According to djm, it uses
IPTOS_THROUGHPUT which is 0x8 not 0x4.
<http://www.gossamer-threads.com/lists/openssh/dev/48410>. (It would be
0x4 if you disregard the "must be 0" field and shift the TOS value one bit
to the right).
And according to the Linux manual page: "IP_TOS (since Linux 1.0) Set or
receive the Type-Of-Service (TOS) field that is sent with every IP packet
originating from this socket. It is used to prioritize packets on the
network. TOS is a byte. There are some standard TOS flags defined:
IPTOS_LOWDELAY to minimize delays for interactive traffic,
IPTOS_THROUGHPUT to optimize throughput..." Nothing about DSCP there.
IETF's attempt to kill it notwithstanding, this is what people actually
use on the Internet.
And PREC 0 is BE.
If you pay attention to PREC, which I don't think anyone does. I've never
seen a packet with PREC bits set either. But I get plenty of packets with
TOS bits set.
I also can't right now remember buying QoS from company which didn't by
default map PREC 5/CS5 to high-priorioty/low-delay (it's used often by
default in phones and conferencing systems). So if you're not going for
DSCP 0x0, you should go with 0x28, i.e. CS5, and it would work in vast
majority of networks which implement QoS, out of the box.
And what networks are those? I don't think you can buy a connection that
actually uses QoS in the UK unless you buy both ends and install your own
routers on them.
Cheers, Chris.
--
_____ __ _
\ __/ / ,__(_)_ | Chris Wilson <chris+sig@xxxxxxxxx> Cambs UK |
/ (_/ ,\/ _/ /_ \ | Security/C/C++/Java/Ruby/Perl/SQL Developer |
\__/_/_/_//_/___/ | We are GNU : free your mind & your software |
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