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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: MPLS VPNs or not?
On Tue, Aug 07, 2001 at 06:55:09PM -0400, Craig Partridge apparently wrote: > There are three separate issues (at least) here, so let's tease them out: > > * Current routing protocols don't do policy. Very right and a known > defect in IP routing (though in part, they don't do it because in > the general case, policy is hard) And policy-based routing everywhere is not scalable. OK, we could argue about the future, but I suspect that no matter how much power we give router owners, they'll come up with policies that use it all. > * Per hop policy decisions can be made more effectively in MPLS than > in IP. Not true in theory unless you want to look very deep in > the packet to identify the policy association, though it may be > true in practice on certain current systems. MPLS doesn't require per-hop policy decisions. Policy decisions only need to be made at the edge, re FEC inclusion. Intelligence at the edge etc. Parallels with the diffserv model of classifying & marking packets at the edge so you only need to look at PHBs in the middle. > * Instantiation of per-hop policy information via MPLS is more scalable > than it would be in IP (not quite said above but an implied issue). > Almost certainly not true (see above about general policy being hard > being why IP doesn't do it). Instantiation of per-hop policy in MPLS consists of forwarding by LSP, except at the edge router. ..Scott (at the IETF)
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