Scavenger classification confusion

[ianwarb]

I am slightly confused as to the scavenger class recommended marking and how it relates to other traffic. The recommendation is to mark BE at IPP/DSCP 0 and mark Scavenger with CS1 (DSCP8)however 8 is above 0 so will surely get priority over BE traffic. Can someone explain this apparent anomaly, thanks.

[afilandro]

Hi Ian,

I think I know the answer to this question. When they started kicking around the Diffserv RFC, they intended for it to include drop-bits and rates based on markings that would be greater than best-effort traffic. So Best-Effort was always DSCP0...I think subsequently thereafter, people needed a "class" or at least a way to differentiate bad/scavenger traffic against everything else...since there was no RFC for anything below 0, they had to standardize on a marking that was unique (and a high enough drop rate) ---so that DSCP8 was chosen. So at least now if you see stuff coming in with a CS1 marking on your routers, you can add a policer to it.

I heard someplace that there was some interest in extending the Diffserv RFC to include less-than-best-effort traffic, but if you really think about it, if you can differentiate that traffic with whatever marking, and then policing it, it really doesnt matter all that much.

:)

[ianwarb]

Many thanks for your response