Steven M. Bellovin writes:
> In message <[EMAIL PROTECTED]>, Brian E Carpenter writes:
> >Indeed. All of this is the same for the DSCP actually, and the
> >assumption is that operators will protect themselves with
> >admission control.
> >
> >(See sections 7.1 of RFC 2474 and 6.1 of RFC 2475 for detailed discussion)
> >
>
> Right. The question now is how to do that. I was about to agree
> strongly with the "must send as zero if not a flow, routers must not modify"
> until I started thinking along these lines. What should a border
> router do with a packet that doesn't meet its constraints? I only see
> three choices: reset the flow label to something locally acceptable,
> drop the packet, or tunnel. But dropping the packet means that flow
> labels can only be used for flows that stay within a particular flow
> label domain, and the tunneling path leads to madness. (Well, perhaps
> to MPLS, but I don't think we want to go down that rathole now.) I'm
> forced to conclude that we have two choices: either we give up on flow
> labels entirely, or we permit them to be modified en route.
First of all, there's nothing that is defined
from which to take action based on the flow label,
so I think this is largely an academic question.
If we suspend some disbelief and posit an edge
device which, say, polices a flow to a particular
rate, why does it follow that the router would
need the ability to rewrite the label? Certainly
in the Intserv case, policers don't rewrite the
5 tuple. Their only option is to change the PHB
or drop it. In diffserv style, it can in addition
to dropping and changing its queuing characteristics,
rewrite the DSCP.
So I guess I just don't see where a policer
would need the ability to alter it. Also:
pragmatically, we can alway change our mind
on the mutability front if it starts life as
*immutable*.
Mike
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