> -----Original Message----- > From: James Kempf [mailto:[EMAIL PROTECTED] > Sent: Tuesday, August 08, 2006 1:26 PM > To: Dave Thaler; Julien Laganier; INT Area > Cc: NetLMM WG > Subject: Re: IPv6 addressing model, per-MN subnet prefix, and broadcast > domain > > Dave, > > RFC 1812 Section 2.2.5.1 defines the case where multiple subnets are > associated with a single interface of a router thusly: > > "The inventors of the subnet mechanism presumed that each piece of an > organization's network would have only a single subnet number. In > practice, it has often proven necessary or useful to have several > subnets share a single physical cable.
Yes the last sentence above is what we mean by multiple subnets on a single link. > For this reason, routers > should be capable of configuring multiple subnets on the same > physical interfaces, and treat them (from a routing or forwarding > perspective) as though they were distinct physical interfaces." The "treat them as though they were distinct interfaces" is just one way to implement multiple subnets on a single link, but it is not the only way or necessarily even the recommended way. The sentence is just saying it should be a configurable option to be able to do it that way. -Dave > Is this what you mean by multiple subnets on a single link? > > jak > > ----- Original Message ----- > From: "Dave Thaler" <[EMAIL PROTECTED]> > To: "Julien Laganier" <[EMAIL PROTECTED]>; "INT Area" > <[EMAIL PROTECTED]> > Cc: "James Kempf" <[EMAIL PROTECTED]>; "NetLMM WG" > <[EMAIL PROTECTED]> > Sent: Tuesday, August 08, 2006 1:13 PM > Subject: RE: IPv6 addressing model, per-MN subnet prefix, and broadcast > domain > > > If I understand the picture at bottom, this is fine. > That is, there can be multiple subnet prefixes per link, > and different hosts may be in different subsets of the > set of subnet prefixes. All of this is fine in the IP > addressing model. > > Section 2.1 of the [draft-thaler-intarea-multilink-subnet-issues] draft > acknowledges this: > > In December 1995, the original IP Version 6 Addressing Architecture > [RFC1884] was published, stating: "IPv6 continues the IPv4 model > that a subnet is associated with one link. Multiple subnets may be > assigned to the same link." > > Thus it explicitly acknowledges that the current IPv4 model has been > that a subnet is associated with one link, and that IPv6 does not > change this model. Furthermore, a subnet is sometimes considered to > be only a subset of a link, when multiple subnets are assigned to > the same link. > > -Dave > > > -----Original Message----- > > From: Julien Laganier [mailto:[EMAIL PROTECTED] > > Sent: Monday, August 07, 2006 6:21 AM > > To: Dave Thaler; INT Area > > Cc: James Kempf; NetLMM WG > > Subject: IPv6 addressing model, per-MN subnet prefix, and broadcast > domain > > > > Hi Dave, and other folks knowledgeable about IPv6 addressing model, > > > > [EMAIL PROTECTED] CCed, please reply only to [EMAIL PROTECTED] > > > > While working on the issues of which addressing model to use in > > NetLMM, I think I got confused with issues involved the IPv6 > > addressing model (or its assumptions.) > > > > I would therefore like to ask you if a potential NetLMM addressing > > model (per-MN subnet prefix [RFC3314]) would, in some situations, > > conflict with the IP addressing model. > > > > Background > > ---------- > > > > Dave's draft on issues involved with multilink subnets > > [draft-thaler-intarea-multilink-subnet-issues] list some assumptions > > of the IP addressing model, but there might be other that are not > > specific to multilink subnets. I'd therefore like to ask you about > > possible conflicts between IPv6 and RFC3314 addressing model. > > > > We are considering the situation of mobile nodes (MNs) attached to a > > NetLMM domain. The NetLMM domain span multiple access links, each > > served by a given access router (AR). A MN attaches to one link, and > > hence to one AR. > > > > ( NetLMM domain ) > > / | | | \ > > AR AR AR AR AR > > / \ \ / \ \ > > MN MN MN MN MN MN > > > > If all of the MNs in the domain uses a common subnet prefix we > > obviously end-up with a multilink subnet, which is problematic as > > described in Dave's draft. Now a simple way to avoid multilink subnet > > issues is to use a per-MN subnet prefix, as in the IETF > > recommendation to 3GPP [RFC3314]. That way, each of the MN moves has > > a different prefix and hence none of the prefix spans more than one > > link, thus avoiding multilink subnet issues. > > > > Issue > > ----- > > > > Such model has however raised a question, which is orthogonal to > > multi-link subnets issues. RFC3314 was proposed for use in a scenario > > where the link between the MN and its AR is point-to-point. Now if we > > consider a broadcast/multicast capable link-layer technology such as > > Ethernet, then we would have a situation in which, on a given link, > > the broadcast domain and hence the link-local scope are larger than > > the any of the per-MN subnet prefixes scope (as illustrated below > > when 3 MNs A, B and C are connected to one such link served by one AR > > R). > > > > A subnet prefix scope: -R-------A------------------ > > > > B subnet prefix scope: -R---------------B---------- > > > > C subnet prefix scope: -R------------------------C- > > > > link-local scope: -R-------A-------B--------C- > > > > L2 broadcast scope: -R-------A-------B--------C- > > > > Do you think that this situation (i.e. link-local scope larger than > > subnet prefix scope) would conflict with the IPv6 addressing model, > > or any of its assumptions? > > > > Many thanks in advance. Best regards, > > > > --julien > > > _______________________________________________ Int-area mailing list [email protected] https://www1.ietf.org/mailman/listinfo/int-area
