Re: [p2pi] ALTO Information Export Service

Reinaldo Penno <> Wed, 29 October 2008 04:23 UTC

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Date: Tue, 28 Oct 2008 21:22:30 -0700
From: Reinaldo Penno <>
To: Salman Abdul Baset <>
Message-ID: <>
Thread-Topic: [p2pi] ALTO Information Export Service
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Cc:, "Woundy, Richard" <>
Subject: Re: [p2pi] ALTO Information Export Service
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How do I interpret its results? For example, first IP addresses I put.

 ./aslookup -r | more

Who owns this prefix? Is it AS7132 (SBC), AS4230(Embratel) or

origin:     AS7132
mnt-by:     MAINT-AS7132
changed: 20030317
source:     RADB

origin:     AS4230
remarks:    -------------------------------------------------
remarks:    For SECURITY issues, please send messages only to
remarks:    -------------------------------------------------
mnt-by:     MAINT-EMBRATEL
changed: 20070222
source:        NTTCOM

descr:         EMBRATEL
origin:        AS28513
mnt-by:        TELMEX-MNT
changed: 20081014
source:        LEVEL3

On 10/28/08 9:05 PM, "Salman  Abdul Baset" <> wrote:

> Mapping IP addresses to AS numbers by quering RIRs:
> -s
> On Tue, 28 Oct 2008, Reinaldo Penno wrote:
>> 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.
>> Thanks,
>> Reinaldo
>> On 10/28/08 4:00 PM, "Woundy, Richard" <>
>> 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:
>>> 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
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