Interactive QoS with `scp'

[Mario Gartner]

Hi!

I experimented with dropbear 2013.62 and its new QoS handling according to the changelog.
While I see the changed behavior when using non-pty ssh connections, I still get the "interactive" TOS in sent IP packets when using `scp'.
My assumption was that scp should be considered bulk/no-pty. Did I miss something?


Here are some command examples and the resulting TOS captured with tcpdump.

# normal ssh --> uses IPTOS_LOWDELAY == OK!
ssh 14.64.1.4
tos 0x10

# option -T for no-pty --> uses IPTOS_THROUGHPUT == OK!
ssh -T 14.64.1.4
tos 0x8

# 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


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


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...


Mario