Re: [p2pi] ALTO Information Export Service

Reinaldo Penno <> Tue, 28 October 2008 23:49 UTC

Return-Path: <>
Received: from [] (localhost []) by (Postfix) with ESMTP id DECBA3A6931; Tue, 28 Oct 2008 16:49:55 -0700 (PDT)
Received: from localhost (localhost []) by (Postfix) with ESMTP id 509903A68D8 for <>; Tue, 28 Oct 2008 16:49:55 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -6.599
X-Spam-Status: No, score=-6.599 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, RCVD_IN_DNSWL_MED=-4]
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id cNx1jbxT57on for <>; Tue, 28 Oct 2008 16:49:48 -0700 (PDT)
Received: from ( []) by (Postfix) with ESMTP id 345913A6805 for <>; Tue, 28 Oct 2008 16:49:44 -0700 (PDT)
Received: from source ([]) by ([]) with SMTP; Tue, 28 Oct 2008 16:49:42 PDT
Received: from ([]) by with Microsoft SMTPSVC(6.0.3790.3959); Tue, 28 Oct 2008 16:48:51 -0700
Received: from ([]) by with Microsoft SMTPSVC(5.0.2195.6713); Tue, 28 Oct 2008 19:48:47 -0400
Received: from ([]) by ([]) with Microsoft Exchange Server HTTP-DAV ; Tue, 28 Oct 2008 23:48:46 +0000
User-Agent: Microsoft-Entourage/
Date: Tue, 28 Oct 2008 16:48:38 -0700
From: Reinaldo Penno <>
To: "Woundy, Richard" <>, John Leslie <>, Stanislav Shalunov <>
Message-ID: <>
Thread-Topic: [p2pi] ALTO Information Export Service
Thread-Index: Ack5IfFnziqzqTA+S7a0lPNtm6F0ogADRzeAAAopHPc=
In-Reply-To: <>
Mime-version: 1.0
X-OriginalArrivalTime: 28 Oct 2008 23:48:47.0861 (UTC) FILETIME=[B896FA50:01C93957]
Subject: Re: [p2pi] ALTO Information Export Service
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: P2P Infrastructure Discussion <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

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

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



On 10/28/08 4:00 PM, "Woundy, Richard" <>

>> 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:
> 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: [] On Behalf Of
> John Leslie
> Sent: Tuesday, October 28, 2008 1:23 PM
> To: Stanislav Shalunov
> Cc:
> Subject: Re: [p2pi] ALTO Information Export Service
> Stanislav Shalunov <> 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.
> 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 <>
> _______________________________________________
> p2pi mailing list
> _______________________________________________
> p2pi mailing list

p2pi mailing list