tree fac0e97f27145aeef62714ac0f50651ef4621df9
parent 424b544fbda963f973da80f884717c3e0a513288
author job@openbsd.org <job@openbsd.org> 1522854737 +0000
committer Damien Miller <djm@mindrot.org> 1522988433 +1000

upstream: Update default IPQoS in ssh(1), sshd(8) to DSCP AF21 for

interactive and CS1 for bulk

AF21 was selected as this is the highest priority within the low-latency
service class (and it is higher than what we have today). SSH is elastic
and time-sensitive data, where a user is waiting for a response via the
network in order to continue with a task at hand. As such, these flows
should be considered foreground traffic, with delays or drops to such
traffic directly impacting user-productivity.

For bulk SSH traffic, the CS1 "Lower Effort" marker was chosen to enable
networks implementing a scavanger/lower-than-best effort class to
discriminate scp(1) below normal activities, such as web surfing. In
general this type of bulk SSH traffic is a background activity.

An advantage of using "AF21" for interactive SSH and "CS1" for bulk SSH
is that they are recognisable values on all common platforms (IANA
https://www.iana.org/assignments/dscp-registry/dscp-registry.xml), and
for AF21 specifically a definition of the intended behavior exists
https://tools.ietf.org/html/rfc4594#section-4.7 in addition to the definition
of the Assured Forwarding PHB group https://tools.ietf.org/html/rfc2597, and
for CS1 (Lower Effort) there is https://tools.ietf.org/html/rfc3662

The first three bits of "AF21" map to the equivalent IEEEE 802.1D PCP, IEEE
802.11e, MPLS EXP/CoS and IP Precedence value of 2 (also known as "Immediate",
or "AC_BE"), and CS1's first 3 bits map to IEEEE 802.1D PCP, IEEE 802.11e,
MPLS/CoS and IP Precedence value 1 ("Background" or "AC_BK").

OK deraadt@, "no objection" djm@

OpenBSD-Commit-ID: d11d2a4484f461524ef0c20870523dfcdeb52181