Interactive QoS with `scp'

[Matt Johnston]

Hi,

> # ssh with command (implies no-pty) --> uses IPTOS_THROUGHPUT == OK!
> ssh 14.64.1.4 "date"
> tos 0x8
> 
> # scp --> Still uses IPTOS_LOWDELAY! i.e. NOT OK(?)
> scp /tmp/file.dat 14.64.1.4:/tmp/
> tos 0x10

That's strange. scp should just be calling "dbclient localhost scp -t destination" - the same as the "date" case. Could you run

strace -f -F -e process scp /tmp/file.dat 14.64.1.4:/tmp/

and check what it's doing?

> [The TOS of the initial packets during connection establishment was 0 and then changed to the mentioned values, which is OK and expected]

Yep, that's intentional to avoid initial roundtrip latency.

> One more thing:
> Using TOS is actually obsoleted. "Modern" implementations should use the DS Field and DSCP classes as described in RFC2474/RFC3260.
> But as long as interactive and non-interactive connections can be identified and separated in the network, I'm fine with that...

Yeah, I couldn't see any benefit though. It's just an extra
configuration option with no sensible default value? (Assume
rfc2597 is the most relevant one).

Cheers,
Matt