Diff Serv QoS Tagging

Does anyone know what protocol canopy tags Diff Serv info with?
(802.1p / mpls / dscp)

I may have answered my own question if anyone cares.

Some Canopy documentation says that they use a 6 bit field in the IP Header, which would mean they use DSCP.

I still don’t understand all this stuff about Code points though, and how to determine which services get priority…

Thanks for posting your findings. After I read your first post I was curious about that myself.

All I can say about the CodePoints is that there are a few you can not change i.e. CodePoint 56 is set to 7 and is reserved for VoiP. I believe you can’t change that priority.

DiffServe and Code Points are right out of RFC 2474, which you can find here.

Cisco has a pretty good tech note describing it here.

Thanks Curtis :slight_smile:

Happy to help!

I’ve gained a treasure of information from this forum. Feels good to pitch in where I can…

So on Canopy, if you want something to have high priority… a 5 is better than 7?

Because all of this says that 5 is express forwarding and 7 is something to do with routing protocols?

To the best of my understanding, yes, a 5 is better than a 7. From the Cisco paper:


The DiffServ standard utilizes the same precedence bits (the most significant bits—DS5, DS4 and DS3) for priority setting, but further clarifies the definitions, offering finer granularity through the use of the next three bits in the DSCP. DiffServ reorganizes and renames the precedence levels (still defined by the three most significant bits of the DSCP) into these categories (the levels are explained in greater detail in this document):

Precedence Level


7 – Stays the same (link layer and routing protocol keep alive)

6 – Stays the same (used for IP routing protocols)

5 – Express Forwarding (EF)

4 – Class 4

3 – Class 3

2 – Class 2

1 – Class 1

0 – Best effort

With this system, a device prioritizes traffic by class first. Then it differentiates and prioritizes same-class traffic, taking the drop probability into account.

The DiffServ standard does not specify a precise definition of “low,” “medium,” and “high” drop probability. Not all devices recognize the DiffServ (DS2 and DS1) settings; and even when these settings are recognized, they do not necessarily trigger the same PHB forwarding action at each network node. Each node implements its own response based on how it is configured.

I think that you can safely say that a lower number is a higher priority, but it seems more specific and complex than that simplification.

RFC 2597 may better illuminate the different settings, but I’m still quite foggy on exactly what it’s saying…

Somebody with a better functional understanding of this please jump in here!