Re: [p2pi] ALTO Information Export Service

[Reinaldo Penno <rpenno at juniper.net>]

I agree with you Rich. Getting an accurate mapping of IP to 'owner' ASs is
not an easy task. Some people spent a lot of time on this. I did not know
this presentation.

Here is a another very good reference:

Towards an Accurate AS-Level Traceroute Tool
Zhuoqing Morley Mao Jennifer Rexford Jia Wang Randy H. Katz
UC Berkeley AT&T Labs­Research AT&T Labs­Research UC Berkeley
zmao at cs.berkeley.edu jrex at research.att.com jiawang at research.att.com
randy at cs.berkeley.edu

In this paper they discuss in detail all the roadblocks to have a traceroute
tool that maps IP to ASs.

Thanks,

Reinaldo


On 10/28/08 4:00 PM, "Woundy, Richard" <Richard_Woundy at cable.comcast.com>
wrote:

>> The routing view which actually matters is the view of the ISP router
> which dispatches the particular packet at a peering point. Thus, IMHO,
> the ISP should usually be the provider of the mapping of IPs to ASNs.
> 
> Before this email, my opinion was that if an ISP wanted to include
> ASN(s) in the policy to be returned by the ALTO service, then the ISP
> should also supply the IP prefix to ASN mappings, so that the combined
> ALTO service guidance came from a consistent information source (the
> ISP). But I didn't have a strong opinion against using a looking glass
> server instead for the IP-to-ASN mappings.
> 
> If I understood John correctly, the looking glass server's view of
> IP-to-ASN mappings may depend on the server's location in the Internet
> topology, and that view may not be equivalent to the view of the ISP
> providing the ALTO service.
> 
> Here is one example: Within one ISP's backbone, there may be a set of
> specific IPv4 prefixes coming from many origin AS's. Within another
> ISP's backbone, these specific prefixes may have been replaced (and
> subsumed) by a single aggregate prefix with a different origin AS (e.g.
> the first backbone). Therefore, the looking glass servers for the first
> and second backbones would differ on the correct origin AS with respect
> to this aggregated prefix.
> 
> Here is a relevant RIPE presentation (from 2003) in which they faced
> similar problems with reporting ASNs in traceroutes:
> http://www.ripe.net/ripe/meetings/ripe-46/presentations/ripe46-tt-as-tra
> ceroutes.pdf. In the scenario of the RIPE presentation, the route
> information in the Internet Routing Registries and in the global BGP
> routes were often at odds with one another; slides 8, 10, and 11
> describe some interesting cases that relate to this discussion about
> looking glasses.
> 
> John, in short, I think you make a very good point.
> 
> -- Rich
> 
> -----Original Message-----
> From: p2pi-bounces at ietf.org [mailto:p2pi-bounces at ietf.org] On Behalf Of
> John Leslie
> Sent: Tuesday, October 28, 2008 1:23 PM
> To: Stanislav Shalunov
> Cc: p2pi at ietf.org
> Subject: Re: [p2pi] ALTO Information Export Service
> 
> Stanislav Shalunov <shalunov at shlang.com> wrote:
>> 
>> We put together a first iteration of a very simple ALTO solution
>> draft.  We hope this will be useful as an example point in the
>> solutions space and thus allow to refine the requirements document and
> 
>> the problem statement.
>> 
>> 
> http://www.ietf.org/internet-drafts/draft-shalunov-alto-infoexport-00.tx
> t
> ] ...
> ] 7.  Mapping IPs to ASNs
> 
>    I expect ISPs will sometimes mean different things by "preferring"
> ASNs. (This is a pretty generic problem with ASNs in ALTO.)
> 
>    ISPs generally peer with a limited number of ASNs, and reach IPs
> "owned" by other ASNs through routes from the ASNs they directly peer
> with.
> 
>    What actually causes an ISP to "prefer" a set of IPs is knowing that
> they will use a route to them through a particular AS they peer with.
> This is _not_ the same as which AS "owns" the IP in question. (Nor is
> "owned by an AS" necessarily a meaningful statement for a CIDR block.)
> 
>    BGP looking-glass views show which ASNs "originate" routes to a
> CIDR block. It is not particularly unusual to find more than one AS
> "originating" such a route. Thus, looking-glass results cannot assure
> that the route a packet will actually follow to reach an IP address
> _ever_ passes through a particular AS.
> 
>    Looking-glass views _will_ generally show "holes" punched in CIDR
> blocks "owned" by one AS for the purpose of balancing traffic to a
> multihomed customer of that AS (even though it may be that _none_ of
> the traffic will actually pass through the "owner" AS). But looking-
> glass views tend to contain routes that are never seen by routers
> not "near the backbone".
> 
>    The routing view which actually matters is the view of the ISP
> router which dispatches the particular packet at a peering point.
> Thus, IMHO, the ISP should usually be the provider of the mapping of
> IPs to ASNs.
> 
>    (This mapping may change several times per second when routes
> "flap", but that's a balancing act the ISP is best able to attempt.)
> 
>    In any case, if ALTO provides ASN "preferences" at all we should
> provide a mechanism for the ISP to perform mapping of IP to ASN.
> (IMHO, at least...)
> 
> --
> John Leslie <john at jlc.net>
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