On Tue, Jul 8, 2008 at 10:15 AM, RJ Atkinson <[EMAIL PROTECTED]> wrote: > In at least some technologies that are being discussed on > this list, the "Network-layer" Identifier does not have > L2 Locator semantics. > > Whether one considers such an Identifier to have L2 > Identifier semantics depends mostly on how one defines > the layers; just as it can be hard to distinguish > between the "top of the network layer" and the "bottom > of the transport layer". Is ARP at the top of layer > 2 or the bottom of layer 3 ? What layer is MPLS in ?
Ran, Rather than get sidetracked by terminology and arguments over the definition of an identifier, lets return to the original point: in IP, layer 3 and above are not tightly bound to the layer-2 address. Because of this, multiple layer-2 addresses can be used during the delivery of an IP packet and the layer-2 addresses in use can change willy-nilly without impacting the function of the IP protocol. Some examples of this in action are: * Proxy ARP * ARP-based failover * Linux will by default send ARP responses for any of it's IP addresses on any interface where it receives an arp request, even if the address is not configured on that interface. On the other hand, layer 4 is tightly bound to layer 3: a session is identified the ports plus the layer 3 addresses. The session does not survive either of the layer-3 addresses changing. -IF- the layer 4 protocols were redesigned in such a manner where this was not the case then the layer-3 address could change willy-nilly as well. This has major implications for address-based route aggregation. I claim they're major enough to solve the route scaling problem. What's the counterexample? Is it impossible to design a protocol that permits layer-4 on different hosts to find each other dynamically as with ARP at the layer2/3 boundary? Is it impossible to design a wide-scale aggregable addressing protocol? Given an optimal address layout, would the topology of the Internet still require too many routes? Would this sort of design induce the same sort of route-policy violations that geographical aggregation does? Such a change would break the hell out of many of the existing network security models. Would the resulting protocols be unsecurable? What's the counterexample? Why -won't- decoupling layer 4 from the layer 3 address permit a -successful- solution to route scaling through topological route aggregation? Regards, Bill Herrin -- William D. Herrin ................ [EMAIL PROTECTED] [EMAIL PROTECTED] 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004 -- to unsubscribe send a message to [EMAIL PROTECTED] with the word 'unsubscribe' in a single line as the message text body. archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg
