Joel/Christian, On Fri, Aug 03, 2007 at 12:38:15PM -0400, Joel M. Halpern wrote: > At 12:27 PM 8/3/2007, Christian Vogt wrote: > >I do agree that, to remain reachable, upgraded edge networks would have > >to use their old locator space in addition to the new ID space. What I > >am concerned about are the following two problems that arise from this: > > > > 1. It defeats all of the benefits of the ID/locator split. > > 2. It makes reliable address resolution infeasible. > > > >Regarding problem 1: The four main benefits envisioned for an > >ID/locator split are the following. > > > > (i) Enabling edge networks to route packets via arbitrary providers. > > (ii) Reducing the network reconfiguration cost related to rehoming. > > (iii) Reducing the size of the global routing table. > > (iv) Reducing the update frequency of the global routing table. All goodness. I would add that there are also a bunch of well-known (and other) security benefits that accrue from a ID/loc split. > >Now, if an edge network is forced to maintain its old locator space in > >addition to new ID space, then /none/ of (i) through (iv) will be > >satisfied. On the contrary, network administration overhead will be > >increased, and the global routing table will become larger. > > Actually, there seem to be quite a few stages between > advertise all locators in BGP, exactly as today > advertise nothing in BGP > > For example, at a later stage in deployment one could easily imagine > advertising only heavily aggregated reachability in BGP, for those > sites that have not upgraded, while using LISP (or other solutions) > for the bulk of ones traffic. That would give significant > benefit without losing connectivity from the non-upgraded world. Right. In addition, these edge networks might not initially go to something like LISP; rather someone might provide an ITR for them (seems like a service someone might like to provide). BTW, I'm not really sure what an edge network is, or what such a distinction buys one (especially given that in practice [implementation], the distinction between core and edge is rapidly disappearing). > >Regarding problem 2: A coexistence of locators and IDs implies that the > >result of address resolution depends on the location of the resolving > >host: Hosts in legacy edge networks MUST obtain legacy locators, while > >hosts in upgraded edge networks SHOULD obtain IDs. > > This is actually somewhat harder. If hosts actually checked > reachability, or really used all the A records they got back, it > might suffice as part of transition to use the EID plus aggregatable > A information. (It's too bad DNS A records do not have preferences > like MX records, but we can't change that now.) Agreed. BTW, I explicitly tried not to introduce the term "legacy locator" which is why I quoted it in my previous message. Let's not go there. Dave
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