suggestion for DSCP codepoint for "less than best effort" (scavanger class) traffic


in the IETF transport area there are discussions on DSCP interconnection between networks. It's quite common that operators clear (bleach) the DSCP codepoints when receiving packets from other operators, turning everything into BE (best effort) traffic. Historically CS1 has been proposed as less-than-best-effort (for instance bittorrent traffic), but my opinion is that this is ill suited as I think it's not incrementally deployable. Some networks might use CS1 as something that has higher priority and it would be hard for them to change this incrementally.

I have proposed a DSCP codepoint that I believe is incrementally deployable and that is 000010, which I think is deployable because it maps to CS0, PRECEDENCE 0, so any kind of equipment that today takes these bits and imposes it into 802.1p, MPLS TC (former EXP) etc, will just map this to regular BE. If explicitly configured, one can match on 000010 and put this in a different queue, for instance that doesn't have much bandwidth guarantees at all.

Since this proposal just comes from my personal experience with equipment in the MPLS/L2/IP world, I'd like to hear wider view/opinion on this and I'll bring it to the TSVWG at the upcoming IETF in Prague July 20-25.

It would be great if there could be an operational document as well, giving recommendations on how to configure the above, and it would be great if it could be done with lots of operator input into the matter.

Given that some networks don't employ QoS, others do but use IPP instead
of DSCP, and others have exaggerated QoS policies that adding a new
profile could be rocket science, it would be interesting to see how this
gets implemented even on the back of a community-agreed spec.

I fear it may follow the same fate as PMTUd. My concern would be around
making sure it does not end up in that bin.