Margaret Wasserman wrote: > > Thanks for the response, Brian. > > > > Are there reasons for preferring to put a flow label inside the > > > IPv6 header? Is this being done on the advice of folks who are > > > standardizing label switching technologies? > > > > >No, because it has nothing to do with label switching. It's much > >more to do with QOS than routing. We know how to use the draft-rajahalme- > >label for Intserv and Diffserv, but it may well have other QOS > >usage as well. It's end2end property is vital for that and completely > >different from the swappable MPLS-type label. > > But, I still don't understand why an IPv6 QoS/diffserv flow label > is "completely different" from an MPLS-type label... > > I do understand that MPLS labels are swapped at each intermediate > node, and that IPv6 flow labels will not be. What are the other > differences? > > Will we still use the IPv6 destination address in each packet to > determine the next-hop router? Or will routers set-up state > regarding the next-hop associated with each flow label?
The "pure" answer is that only the address will be used, i.e. the address is necessary & sufficient. But QoS-aware routing can do whatever it wants; it can look at any non-encrypted field it chooses. I would expect to see QoS-aware routing using the DSCP which is only 6 bits and defined identically for IPv6 and IPv4, rather than using the 20 bit flow label. However, if you want a multiprotocol solution to this, we have one already that does what you describe, and it's called MPLS. > > If the former, then I understand the difference. An intermediate > router would need to read the IPv6 (or IPv4) header, anyway, in > order to forward the packet. The IPv6 flow label would just be > some additional information to influence packet queuing or > processing. Exactly; that's the "pure" architecture. > > However, if the latter (routers save next-hop state based on flow > labels), wouldn't it be better to develop a mechanism that could > work with both IPv6 and IPv4, so that routers will not have to > behave differently for IPv6 and IPv4 packets? Yes, hence MPLS. The one gap in MPLS is that the "QoS" bits are technically "experimental" bits - but the diffserv-to-MPLS mapping makes it pretty clear how to use them for QoS. > > If I seem to be missing an important point or concept, please send > some hints or pointers. I don't think you are. One intent of draft-rahalme- is to clarify that the IPv6 flow label is *not* a routing label. Brian -------------------------------------------------------------------- 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] --------------------------------------------------------------------
