[olug] ssh/scp does tag traffic for QoS

[neal rauhauser]

  A quick examination of a file scp and a short ssh session to a remote
hosts shows the following:

DSCP (differentiated services code point) for ssh traffic sets the whole
ToS or DS byte to zeros, while the scp traffic sets the byte to 0000
1000.

 A quick review of the Cisco Press QoS book shows that there are three
bits of ip precedence and four bits for ToS or type of service, with one
bit being unused.

 The newer DSCP uses the first six bits with the last two bits unused.

Here is a short table showing the relationship:

precedence 0		000 000
precedence 1		001 000
precedence 2		010 000
precedence 3		011 000
precedence 4		100 000
precedence 5		101 000
precedence 6		110 000
precedence 7		111 000


  So the OpenSSH app very politely uses nothing but precedence 0 for the
sake of older networks, but sneaks in a bit of information in what would
be the ToS nibble to allow those using diffserv to treat the two types
of traffic differently.

  I am off to tear out some precedence based stuff and switch to DSCP
for traffic marking ...




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