Re: [v6ops] [tcpm] Flow Label Load Balancing

[Erik Kline <[e-mail]>]

> > Please include requirements for both hosts and network nodes. If there
> > is going to the be a requirement that hosts MUST make a 1:1 mapping to
> > a transport connection and the flow label MUST be consistent for the
> > life of connection, then I would expect there to also be a requirement
> > that the flow label MUST be immutable by all devices in the path-- in
> > particular the requirement of RFC6437 would need to be updated: "A
> > forwarding node MUST either leave a non-zero flow label value
> > unchanged or change it only for compelling operational security
> > reasons..."-- if hosts are not allowed to change a field they are
> > primarily responsible for setting, then the network should not be
> > allowed to modify it either.
>
> I don't recall _(of the top of my head) why we ended up making the field
> mutable ("SHOULD NOT  be modified" rather than "MUST NOT.."). IIRC, it
> had to do with allowing middle-boxes to mitigate FL-based covert
> channels.  If that's the case (Brian CC'ed) then, in retrospective, that
> seems to have been a bad idea.  -- I was part of the discussion, so I
> take my share of blame. :-)

My understanding/recollection is that since there were never any
restrictions on modification of the flow label from the very beginning
it wasn't super meaningful to try to close the barn door after all
these years.