On Wed, Feb 09, 2011 at 06:34:32PM -0800, Philip Prindeville wrote: > The default values for OpenSSH QoS markings are wrong. > > They use 'lowdelay' and 'throughput' for interactive and bulk traffic, > respectively. > > Unfortunately, these values were retired in 1998 when the low-order 2 bits of > ToS field were repurposed for DSCP: originally RFC-2474 marked the lower 2 > bits as 'CU' (currently unused), but they were eventually designated as ECT > and CE in RFC-2481 and then as ECT0 and ECT1 in Explicit Congestion > Notification (RFC-3168). > > The upshot of all this is that marking traffic with these obsolete markings > could mean that not only is the traffic not handled as desired, but it's > handled in a highly detrimental fashion (for instance, the RFC-791 > designation of 'lowcost' collides with the ECT0 and CE values of RFC-3168 as > well as that of obsolete RFC-2481). > > I'm surprised that this wasn't fixed a lot sooner (like a decade ago). > > For whatever reason, while OpenSSH has accepted my patches for allowing the > configuration of QoS, the default values are still the obsolete ToS fields > from RFC-791 which is dangerously ancient (that part of the patch was left > out). > > The patch here itself is fortunately trivial. > > DSCP markings will be ignored in the majority of equipment not implementing > it or where it has not been enabled. > > If you're forced to interoperate with some seriously braindead gear like a 10 > year-old bargain Taiwanese firewall or router that discards traffic with > these bits set (extremely rare but not unheard of), then your best bet is to > turn off QoS marking all together as: > > IPQoS CS0 CS0 > > in both /etc/ssh/ssh_config and sshd_config. > > A fix has been submitted for OpenSSH: > > https://bugzilla.mindrot.org/show_bug.cgi?id=1856
With all respect real world usage is different. The TOS field was defined in RFC-791 and is still used today by many people including the pfifo_fast egress scheduler (the default) in the Linux kernel. As just the IP precedence part was ever used or if used with care it doesn't collide with ECN. I don't see why it is obsolete, many organizations (including my University) honours those fields internally. In the outside Internet almost nobody honours TOS nor DSCP. IMHO the correct answer is Active Queue Management (ACM) with ECN in the border routers and something simple as TOS or VLAN priority internally. Facts: All Linux routers by default honours the TOS field. Big routers as used in the transport links in the Internet doesn't honour neither TOS nor DSCP (net neutrality remember?). DSCP does not obsolete TOS in the real world. IPv6 does not obsolete IPv4 in the real world. Many software supports TOS field but not DSCP. In contrast with your point of view I believe TOS is used widely than DSCP so current behavior should be preserved unless the admin wish to change it. _______________________________________________ openwrt-devel mailing list [email protected] https://lists.openwrt.org/mailman/listinfo/openwrt-devel
