> On Thu, Aug 16, 2001 at 08:44:59AM -0500, Brian E Carpenter wrote:
> > I think the WG needs to decide once and for all whether the flow
label
> is
> > a) a CATNIP or MPLS-like routing handle
> > or b) a QOS hint for intserv only
> > or c) a QOS hint for intserv and diffserv
> > or d) a waste of bits
I think that the most useful use is probably (c). Option (a) is not
terribly interesting: if you want to do MPLS, just insert an MPLS
header; MP in MPLS stands for multi-protocol, which means that MPLS is
always going to have a "layer of indirection" for v4, v6, and whatever
else the ISP wants to run on it. Option (b) really means "a set of
random bits" and is not terribly useful either: it would require that
the routers trusts the random generation in the hosts, which is not
going to happen (the trust, I mean.)
Option (c) really means "tell me something useful about the content of
the packet so I can use it for classification." Suppose I place here the
port number that identifies the service, e.g. 25 for mail, 80 for web,
etc., plus an indication of whether this is UDP or TCP. This plus the
addresses would enable some easy filtering into intserv or diffserv
classifications, without requiring that the router go deep into the
header chain. It would enable easy traffic statistics. It would be easy
to implement for the host (pick the lowest of dest or source port.) It
would work even if the packet is encrypted. We could reserve values for
specific traffics, e.g. RTP-audio, RTP-video. It would work even if we
use ESP. From an information theory point of view, this looks much more
useful than either random bits or null values.
Indeed, the bits will have to be set by the host. But then, so are the
port numbers. Nothing prevent cooperating hosts from running NFS over
port 80... In fact, if the router is willing to inspect the full header
chain, it could rewrite the bits to a "trusted" value. Also, some hosts
may not be willing to provide the information, e.g. when they actually
want to hide the nature of the encrypted traffic; these hosts could use
a null field, which would be classified to some default rule by the
diffserv filters (you cannot have it both ways.)
Count my vote for (c).
-- Christian Huitema
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page: http://playground.sun.com/ipng
FTP archive: ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [EMAIL PROTECTED]
--------------------------------------------------------------------
