If I mark a packet at a edge location with DSCP, does anyone know if ISPS (or in a general sense, middleboxes) strip or modify the DSCP header on UDP packets before they reach another edge location? Most interesting to me is residential to residential.

EDIT: I don't expect the ISP to honor them (Netflix, why didn't you just mark your packets? /sarcasm); I just hope the packets remain unmodified from edge-to-edge.

I'd be interested in answers such as:

  • I've seen it before, but I have no idea how widespread it is
  • It happens a large percentage (> 10%)
  • It does not happen much (< 10%)
  • Rare (< %1)

I know this question is awfully hard to answer unless you have tried to do this, but I figured I'd ask.


This is impossible to speak authoritatively on, but in my experience, the vast majority of ISPs ignore QoS and DSCP headers, and with good reason. If they respected those headers, they would quickly become meaningless as everyone just starts to mark all their packets as EF or AF or somesuch.

The only way to have true end-to-end QoS is to run the entire network yourself.

  • I expect them to ignore them. I'm just hoping they are preserved in transit... but let me update my question to make that clear.
    – sethcall
    May 8 '14 at 19:57

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