that 4byte ASN you were considering...

Michael.Dillon at Michael.Dillon at
Tue Oct 10 08:44:17 UTC 2006

> > - 'Canonical representation of 4-byte AS numbers '
> > 
> and what is good or bad about this representation?  seems simple to me. 
>   and having one notation seems reasonable.  what am i missing?

It breaks any applications which recognize IP address-like 
objects by seeing a dot in an otherwise numeric token.
For the purposes of parsing a string into internal 
representation, an application can treat IP addresses,
netmasks and inverse masks identically.

We all know that the Internet is awash in homegrown scripts
written in PERL or TCL or bash or Ruby or Python. It is likely
that many authors have, in the past 15 years, written scripts
which contain regular expressions like "[0123456789.]*" to
match a string containing only digits and the period. Those
scripts will be confused by this AS number notation. Also,
any script which "recognizes" IP address-like objects when
it hits the first period in a numeric string.

The real question is what does the notation 1.0 add that the
notation 65536 does not provide?

All I can see is that it adds the risk of broken scripts and 
the confusion of AS numbers that look like decimal numbers.
If the IETF had really wanted to create a universal notation
then they should have recommended that AS numbers be
represented in the form AS65536 which is completely

When IP addresses were created, it was important to indicate
the boundaries between the network number and the host address.
Originally, the periods represented this boundary for the
three classes of IP address, class A, class B and class C.
Long ago, we removed this classfulness attribute, but the
notation remains because lots of applications expect this
notation. So why on earth are we changing AS number notation

--Michael Dillon

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