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If my application is using DSCP values, and on the way some packets may be re-tagged by network equipment or other things. The problem is that the network equipment may just talk old-style ToS, meaning it thinks it can change just the Prio bits or the ToS-bits and all will be well.

But all is not well! What do I do with this ToS-byte value that has a value that doesn't have a DSCP mapping when I need to present it to the user?

I see three options:

Present the ToS-byte in numeric format

E.g.: ToS=184.

Yeah... thanks. Not user-friendly.

Present as DSCP if possible, but if no mapping exists, present both fields from that

E.g.:

  • Prio=1,ToS=lowdelay,throughput
  • DSCP=AF21 (mapping exists)

Always present ToS, and present DSCP mapping if possible

E.g

  • Prio=6,ToS=lowdelay,throughput,DSCP=EF
  • Prio=0,ToS=lowdelay,throughput

Any better way?

Extra notes

  • Yes, I know end applications can't expect to have the ToS intact over the internet
  • the numbers above may be inconsistent. I don't care, you know what I mean.