IPQoS

[Saku Ytti]

On (2014-02-13 15:51 +0000), Chris Wilson wrote:

Hi Chris,

> 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.

In real networks TOS is either read as PREC or DSCP. So in real networks it's
either PREC 0 or DSCP 0x4. Neither seem desirable.

> 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.

SCP/SFTP should be different than interactive, according to docs.
So Interactive definitely is /DSCP/ 0x4 or PREC 0.
You can easily check this in tshar:
[ytti at ytti.fi ~]% sudo tshark -Vc 3 port 22|grep DSCP
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
    Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))


> Nothing about DSCP there. IETF's attempt to kill it notwithstanding,
> this is what people actually use on the Internet.

No. This type of marking is not used.

> 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.

As PREC is 3 bits, which is only thing you have in 802.1p and MPLS TC, it's
very commonly used.
Both PREC and DSCP are common, nothing else is in practical terms ever used.
And PREC+DSCP have same meaning for the left most 5 bits.

> 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.

In UK you can talk to BT. If you'll setup NNI there and ask in RFQ for their
QoS, I'm sure you'll find what I said applies.

-- 
  ++ytti