I-D Action:draft-azinger-scalable-addressing-00.txt

Brian E Carpenter brian.e.carpenter at gmail.com
Fri Oct 1 02:11:31 CEST 2010


On 2010-10-01 09:51, Gert Doering wrote:
> Hi,
> On Thu, Sep 30, 2010 at 09:37:23AM -0700, Tony Li wrote:
>> So if you have N entries then your network admins won't bother to make them work?
>> Seems to me like you need new network admins.
> What exactly can the network admin do here?
> Let me try to illustrate this with a specific example.  No complex policies
> for now, just focusing on "shortest path to destination".
> There's a source prefix S1 that is routed via ISP 1, and a source prefix 
> S2 that is routed via ISP 2 (both prefixes coming from the respective 
> ISP's PA space, so BCP 38 filters will require that source address 
> selection automatically selects egress ISP).
> Destination prefix D1 is connected to peer of ISP 1, while destination
> prefix D2 is connected to something 20 hops behind ISP 2 (assuming that
> "20 hops" means "more latency, less bandwidth", for the simplicity of
> the model).
>     +--- S1 === ISP 1 === ISP X ======== D1 ---+
>   source         (*)                         destination
>     +--- S2 === ISP 2 --- ISP A, B, C -- D2 ---+
> How exactly is the end host supposed to know that "S1->D1" is good, while
> "S2->D2" is bad and "S1->D2" is very bad?  (Assume that "use the longest
> sequence of common bits in the addresses" won't help, which is the normal
> case when crossing RIR regions).

The only reasonable answer to this question is (IMHO) trial and error.

For some indication of what that means in practice and at large scale,
please see:

A Performance Study on REAchability Protocol in Large Scale IPv6 Networks, Habib Naderi and Brian Carpenter, Second
International Conference on Computer and Network Technology (ICCNT 2010), Bangkok, (April 2010) 28-32.

at http://www.cs.auckland.ac.nz/~brian/iccnt2010_reap.pdf

This is large scale simulation, but recently Habib has run small scale
lab tests with real code, giving comparable results.


> If I have a single S and D prefix, the end host does not *need* to know,
> and the network *will know* that the path via ISP 1 to its peer to D is 
> shorter than via ISP 2.
> I hope I have succeeded this time in explaining where "we the operators"
> see a gap in the N*M model - and that has nothing whatsoever to do with
> "network admins not being up to the job".   
> Gert Doering
>         -- NetMaster

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