Hi Robin I'm very new to this list, so apologies if I'm not posting in a correct format / method. My very simple question is this:
The paper discusses connectivity to AS's and a method of 'guessing' where an AS is, at the advantage of not needing to store as much topographical information. Atleast that is my take on it.. The thing I don't get is how does that relate to prefixes. Is the implication that the router will keep just a list of origin AS's and the prefixes advertised by each, as opposed to full path information? Cheers Heath On 16 September 2010 12:33, Robin Whittle <[email protected]> wrote: > Short version: I think this article has nothing to do with > Internet routing and so does not provide any > significant insights into or practical solutions > to the routing scalability problem. > > > This article: > > Sustaining the Internet with Hyperbolic Mapping > http://www.nature.com/ncomms/journal/v1/n6/full/ncomms1063.html > http://www.nature.com/ncomms/journal/v1/n6/pdf/ncomms1063.pdf > > doesn't seem to be relevant to AS networks and the BGP-based > interdomain routing system as I understand them. Nor does it appear > to address the problems we have identified - a more scalable method > than the current BGP-based DFZ for providing multihoming, inbound TE > (traffic engineering) and mobility. > > The biggest challenge, I think, is mobility for billions of devices, > each responding to its own IP address, so it can interoperate with all > other hosts using standard stack and application protocols - with > generally optimal or close to optimal paths and session survival via a > persistent IP address, no matter how the "care of" address(es) change. > The only way I can see of doing it is TTR Mobility: > > http://www.firstpr.com.au/ip/ivip/#mobile > > To see my understanding of the goals of scalable routing, please see > section 17.2 of: > > http://www.ietf.org/mail-archive/web/rrg/current/msg06219.html > > > My sense that the article's premises don't accord with reality begins > with the 3rd paragraph: > > The scaling limitations of the existing Internet routing stem > from the requirement to have a current state of the Internet > topology distributed globally. > > This doesn't accord with my understanding. BGP doesn't generate or > distribute a map or anything resembling "the current state of the > Internet". It is simply a method by which the routers can work > together so that each router can, decide which neighbor to forward a > packet to, based on the shortest BGP-advertised prefix the destination > address matches. This is done in a manner by which outages and > topology changes result in changed route advertisements by each > router, and so to changed choices and further changes of route > advertisements by other connected routers. > > For some routers - such as those where "the rest of the Internet" is > reached by a single neighbor, this means that packets addressed to > pretty much every BGP advertised prefix are all sent to one particular > neighbor. For other routers in the "DFZ" (Default-Free Zone), there > will be two or more neighbours which the router decides are the best > ones to handle packets addressed to "the rest of the Internet" (that > is, the prefixes which are not ones this router handles itself). > > Such global knowledge is unavoidable, as routing has no source > of information other than the network topology. > > I think this too is incorrect. > > The BGP routing daemon in each BGP router certainly does have another > source of information: the routes advertised by its neighbours. This > is what it uses. No BGP router has a clue about topology. > > Routing in these conditions is equivalent to routing using a > hypothetical road atlas, which has no geographical information > but merely lists road network links, which are pairs of > connected road intersections, abstractly identified. > > This describes a text-form of a map, similar to a printed circuit > board netlist - where distances between connected items are > irrelevant, but the total set of connections is specified exactly. > > This has nothing to do with how a BGP router chooses the best path for > packets addressed to a given BGP-advertised prefix. There's nothing > resembling a road map or any other map. There's just a bunch of > advertised routes from neighbours, each with its own list of ASes > which must be traversed to reach the destination. Then the router has > its BGP algorithm and local policy for choosing one of these. It then > advertises this path to its other neighbours, perhaps with extra AS > numbers added. > > So how does the rest of the article relate to the Internet in general, > or to the interdomain routing system in particular? As far as I can > see, it doesn't. > > How would this approach be adopted? > > What changes to routers would be required? > > How could this work with BGP? Modifications to BGP, creating a new > network to replace the BGP-based DFZ? > > Why would anyone adopt it? > > When would they derive any benefits? After the rest of the world > adopts it too? > > If it was adopted, how would ASes get their routers to implement the > policies they current set for them? > > How would this provide multihoming to more end-user networks? I guess > this would have to be either without requiring each to have an ASN, or > allowing millions of such networks to get an ASN, but somehow have > this not matter. > > How would mobility be achieved in a robust and scalable manner, for > hundreds of millions or billions of devices - with IPv4 or IPv6? > > > As far as I can see, this is a paper about some new approach to > constructing maps in coordinate systems which do not resemble ordinary > Cartesian coordinates. I guess this is of interest to some folks - > but I don't agree with the central premise that these techniques are > relevant to Internet routing or to a new approach to routing which > would better meet the needs of ASes. > > Can anyone point out exactly why the techniques in this article could > help with scalable routing? Without using an analogy, such as "The > Internet's routing system operates like a road map. We have developed > an improved way of making a map for this purpose." - because that > analogy is false. > > - Robin > _______________________________________________ > rrg mailing list > [email protected] > http://www.irtf.org/mailman/listinfo/rrg >
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