Inevitable death, was Re: Verizon Public Policy on Netflix

Fred Baker (fred) fred at
Sat Jul 19 00:32:18 UTC 2014

On Jul 14, 2014, at 4:32 PM, Scott Helms <khelms at> 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 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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