Excerpts from Dow Street on Fri, Apr 03, 2009 10:51:40AM -0700: > On Apr 3, 2009, at 12:55 AM, Tony Li wrote: >>>> locator A locator is a name that has topological sensitivity at a >>>> given layer and changes if the point of attachment at that >>>> layer changes. By default, a locator refers to layer 3. >>>> It is also possible to have locators at other layers. >>>> Locators may have other properties, such as their scope >>>> (local or global (default)) and their lifetime (ephemeral >>>> or permanent (default)). >>> It is this "point of attachment at that layer" phrase that is still >>> problematic. If a host disconnects from one place on an ethernet >>> segment and connects to another, it can still be reachable without >>> changing it's IP address. Are you defining this as not changing the >>> point of attachment (in terms of layer 3)? >> >> _Exactly_. If you change ports on your local Ethernet switch, then >> you've only changed the L2 topology, and done nothing at all at layer >> 3. > > I am ok defining things this way. To ensure we're on the same page, > this means that only the network part of an IP address (from the > perspective of the host) can ever be considered a locator, right? > > Also, since the mask that is in effect (for forwarding) at various > points in the topology differs, then the part of the IP address that we > can call a locator also differs at various points in the topology.
Ok now we get into the sticky business of locators versus forwarding directives, which we haven't explored and don't have to yet. IMHO a locator names a point of attachment ... but more or less information can be used for forwarding a packet at various points along a path. > I am trying to get at this property of "relative flatness" of > various names and/or parts of the IP address at different points of > the topology, even if we are only talking about familiar, > aggregation based approaches to scalability. > > In other words, if we say that: > > (a) on an ethernet segment (that maps to only a single prefix in the > IP routing system), only the network part of the IP address of > connected hosts is considered to be a (L3?) locator, then (b) a > similar property exists closer to the "middle" of the topology/ > routing system if aggregation is used. > > In (b), more specific prefixes "hidden behind" the aggregate are > topologically flat from the perspective of processes that are only > aware of the less-specific, aggregate mask. > > I think maybe you are accounting for all of this relative-ness with > the phrase "attachment point at that layer"? The relative flatness thing is cool, but you're both right IMHO. At a particular "layer" (whatever that is), points of attachment have unique names, but that's independent of routing and topology, which can impose various degrees of hierarchy on the PoAs. Scott _______________________________________________ rrg mailing list [email protected] http://www.irtf.org/mailman/listinfo/rrg
