[Flent-users] DSCP / ToS

Pete Heist peteheist at gmail.com
Mon Feb 19 11:23:42 EET 2018


> On Feb 18, 2018, at 7:48 PM, Pete Heist <peteheist at gmail.com> wrote:
> 
>>> This would break —dscp’s current behavior, so I would increment the
>>> version number when I do it, and save it for v1.0 in case there are
>>> other breaking changes.
>> 
>> Well, that means Flent would need to deal with this case and detect
>> which version of irtt is available; which IMO goes into the 'too much
>> effort' category ;)
> 
> I hear you. :)

So my latest idea is to not break the current behavior, and rather:

1) Add the text values as described before.

2) Return an error if a value is passed in with either of the two LSBs set to 1. That will save people in many cases who make the same mistake I did of passing in the DSCP value rather than the whole DS field.

3) If ever people really need to set what is currently the ECN bits, add a new flag at that time, but they really shouldn’t be doing that.

Flent should be fine since it doesn’t pass in values with the ECN bits set.

Incidentally, I found that yes, Go lets you set whatever you want in the DS/ToS field, but somewhere along the Internet route from the office to my house, all the bits except the ECN bits are set to 0, so something, somewhere is washing the field in this direction only. So apparently, “DS field washing" happens sometimes as well…





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