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Re: Inevitable death, was Re: Verizon Public Policy on Netflix
From: "Fred Baker (fred)" <fred () cisco com>
Date: Sat, 19 Jul 2014 00:32:18 +0000


On Jul 14, 2014, at 4:32 PM, Scott Helms <khelms () zcorum com> wrote:

I continue to vehemently disagree with the notion that ASN = ISP since
many/most of the ASNs represent business networks that have nothing to do
with Internet access.

And there are a number of ISPs with multiple ASNs.

If you look up the history of the term, "Autonomous System" is used without definition in most of its earlier RFCs, 
such as 820, 827, and 1105. In short, though, it is a network that connects to other networks using a routing protocol 
such as EGP or eBGP. The best formal definition I have seen involves "a collection of physical networks under common 
administration which are reachable from the rest of the Internet by a common route." The quote is from RFC 1000 and 
refers to the domain of a prefix, but it's pretty close. An "Autonomous System Number" is a creature of EGP or BGP 
Routing, and identifies such a system.

If you look at http://bgp.potaroo.net/as6447/ and search for “AS numbers”, and you happen to be looking at exactly this 
instant (it changes), you’ll find that AS 6447 sees 47879 individual AS numbers in the Internet, of which 40339 show up 
*only* as origins (and therefore have to do with the AS a source or destination of traffic), 236 *never* show up as end 
last AS in an AS Path (and therefore are *always* transit), and 7304 that are sometimes origin and sometimes transit. 
To my small mind, an AS that functions as an ISP if highly likely to show up as a transit network, and an AS that never 
shows up as transit is very likely to be multihomed or to have justified its AS number on the basis of plans to 
multihome. Of course, one will also find that 30134 AS’s are origin AS’s visible through exactly one AS path, which 
says that at this instant they’re not actually multihomed.

No, AS != ISP. An AS is a network that needs to be identifiable in global routing but would be entirely reachable even 
if it had exactly one link with some other network.

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