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Re: The internet architecture

2008-12-24 13:50:50
On Dec 22, 2008, at 10:51 PM, macbroadcast wrote:
IP does not presume hierarchical addresses and worked quite well without it for nearly 20 years. IP addresses are topologically independent. Although since CIDR, there has been an attempt to make them align with aspects of the graph.
Ford's paper does not really get to the fundamentals of the problem.

I would suggest that deeper thought is required.

would like to know bryans  opinion

I think I missed some intermediate messages in this discussion thread, but I'll try. :)

IP addresses are just an address format (two, actually, one for IPv4 and another for IPv6); their usefulness and effectiveness depends on exactly how they are assigned and used. CIDR prescribes a way to assign and use IP addresses that in theory facilitates aggregation of route table entries to make the network scalable, _IF_ those addresses are assigned in a hierarchical fashion that directly corresponds to the network's topology, which must also be strictly hierarchical in order for that aggregation to be possible. That is, if an edge network has only one upstream provider and uses in its network only IP addresses handed out from that provider's block, then nobody else in the Internet needs to have a routing table entry for that particular edge network; only for the provider. But that whole model breaks down as soon as that edge network wants (god forbid!) a bit of reliability by having two redundant links to two different upstream providers - i.e., "the multihoming problem", and hence all the concern over the fact that BGP routing tables are ballooning out of control because _everybody_ wants to be multihomed and thus wants their own public, non-aggregable IP address range, thus completely defeating the scalability goals of CIDR.

For some nice theoretical and practical analysis indicating that any hierarchical CIDR-like addressing scheme is fundamentally a poor match to a well-connected network topology like that of the Internet, see Krioukov et al., "On Compact Routing for the Internet", CCR '07. They also cast some pretty dark clouds over some alternative schemes as well, but that's another story. :)

But to get back to the original issue, CIDR-based IP addressing isn't scalable unless the network topology is hierarchical and address assignment is done according to network topology: i.e., IP addresses MUST be dependent on topology in order for CIDR-based addressing to scale. But in practice, at least up to this point, other concerns have substantially trumped this scalability concern: edge networks want fault tolerance via multihoming and administrative independence from their upstream ISPs, so they get their own provider-independent IP address blocks for their edge networks, which are indeed topology- independent (at least in terms of the assignment of the whole block), meaning practically every core router in the world will subsequently have to have a separate routing table entry for that edge network. But this only works for edge networks whose owners have sufficient size and clout and financial resources; we're long past the time when an individual could easily get his own private Class C address block for his own home network, like I remember doing a long time ago. :) So small edge networks and individual devices still have to use IP addresses assigned to them topologically out of some upstream provider's block, which means they have to change whenever the device moves to a different attachment point.

So in effect we've gotten ourselves in a situation where IP addresses are too topology-independent to provide good scalability, but too topology-dependent to provide real location-independence at least for individual devices, because of equally strong forces pulling the IP assignment process in both directions at once. Hence the reason we desperately need locator/identity separation: so that "locators" can be assigned topologically so as to make routing scalable without having to cater to conflicting concerns about stability or location- independence, and so that "identifiers" can be stable and location- independent without having to cater to conflicting concerns about routing efficiency.

As far as specific forms these "locators" or "identifiers" should take, or specific routing protocols for the "locator" layer, or specific resolution or overlay routing protocols for the "identity" layer, I think there are a lot of pretty reasonable options; my paper suggested one, but there are others.

Cheers,
Bryan

merry christmas

Marc


i believe that "Kademlia " [ 1 ] for example and the technologies
mentioned in the  linked paper [ 2 ]
would fit the needs and requirements for a future proof internet.


[ 1 ] http://en.wikipedia.org/wiki/Kademlia
[ 2 ] http://pdos.csail.mit.edu/papers/uip:hotnets03.pdf
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