Hi Iljitsch, I agree with many of the points you have raised in your note. In my draft on "Tunneled Inter-domain Routing" (TIDR) that I sent to the IETF a year ago I covered some of these points. Please see below.
2007/12/17, Iljitsch van Beijnum <[EMAIL PROTECTED]>: > > It seems to me that the basic architecture behind proposals like LISP > is that we separate two things: > > 1 the dynamic inter-AS connectivity (I'll call this the ground floor) > 2 the mapping from prefixes to ASes (I'll call this the second floor) > > Where 2 itself can be split into: > > 2a the fairly static mapping of prefixes to a set of ASes > 2b the dynamic reachability status of each individual prefix->AS > relationship > > LISP is of course somewhat messy because it wants to be highly > backward compatible. In a more radical approach, there isn't even any > reason for (locator) addresses on the ground floor to be globally > unique: see HRA. In TIDR I proposed to use a specific set of addresses for locators (240.0.0.0) that would be assigned to transit AS-es. Transit AS-es would then originate "locator prefixes" that would be use for the dynamic inter-AS connectivity of the "ground floor". One of the main benefits of this is the protection of the inter-domain routing infrastructe because a packet coming from a non-transit AS with destination within the 240.0.0.0 block will be stopped as it enters the inter-domain routing infrastructure. In other words the first non-transit AS will discard that packet. And a transit AS will never accept IP packets with an IP destination in this range UNLESS it is a tunneled packet. Doing routing calculations per prefix rather than per AS could be > considered a design flaw in BGP. For some time now, the number of In TIDR we have the possibility of announcing one or more "locator prefixes" per AS. prefixes per AS has been stable at close to 8.5. Interestingly, new > ASes tend to have far fewer than 8 prefixes, so what's really > happening is that the influx of new ASes and the addition of new > prefixes coincidentally happen at the same rate. In the two floor > system, we immediately gain an order of magnitude in processing > reduction, but this is a one time thing that may not even translate to > IPv6, where the AS-to-prefix ratio is about 1.4. the real savings will > have to come from the ability to prune leaf ASes from the ground > floor: Pruning of leaf AS-es is the base of the reasoning that I followed in the TIDR draft. Leaf AS-es don´t participate in the inter-domain packet forwarding, while at the same time contribute to the size of the global BGP table. They also consume AS numbers. They don't play in the football team but they have a number reserved for their shirt. :-) And finally, they are 5/6 of the total number of AS-es, roughly speaking. rather than map a prefix to a single leaf AS, we need to map a > prefix to multiple transit ASes, or we're stuck with the one-time gain > if we assume the number of prefixes per AS isn't going to go up. (Some > people argue that this is exactly what will happen as the IPv4 space > fragments when it runs out, in my opinion, this isn't all that likely.) In TIDR, "identifier prefixes" of a leaf AS can be mapped by all the upstream ISPs. Only transit AS-es are allowed to map "identifier prefixes" to "locator prefixes". > > Another thing that slightly worries me is that LISP is only focussed > on IP-in-IP tunneling, ignoring all the work that has been done on > MPLS, I think this point is important. In TIDR one can specify several tunneling techniques, IP-in-IP, GRE, or even an MPLS label. Two peering AS-es could announce between them the mapping of "identifier prefixes" to specific MPLS labels. Regards, Juanjo
