that 4byte ASN you were considering...

Tue Oct 10 15:24:56 UTC 2006

On Oct 10, 2006, at 4:34 AM, Michael.Dillon at btradianz.com wrote:

>
>> Well, it will break an applications that considers everything
>> consisting of numbers and dots to be an IP address/netmask/inverse
>> mask.  I don't think many applications do this, as they will then
>> treat the typo "193.0.1." as an IP address.
>
> An application using "[0123456789.]*" will not break when it
> sees the above typo. 193.0.1. *IS* an IP address-like object
> and any existing code will likely report it as mistyped
> IP address or mask.
>
Actually, most code will parse it as equivalant of 193.0.0.1.

Most of  the IP address parsers I have encountered will do
zero insertion in the middle, such that 10.253 is parsed the
same as 10.0.0.253, 10.3.24 is parsed as 10.0.3.24, 192.159.8
is parsed as 192.159.0.8, etc.  I'm not saying I think this is
necessarily good, but, it is the behavior observed.

>>> The real question is what does the notation 1.0 add that the
>>> notation 65536 does not provide?
>>
>> It is (for me, and I guess most other humans) much easier to read and
>> remember, just as 193.0.1.49 is easier to read and remember than
>> 3238002993.  It also reflects that on the wire there are two 16
>> bit numbers, rather than 1 32-bit number.
>
> In my experience, ISPs do not transmit numbers by phone calls
> and paper documents. They use emails and web pages which allow
> cut'n'paste to avoid all transcription errors. And I know of no
> earthly reason why a general written representation needs to
> represent the format of bits on the wire. How many people
> know or care whether their computer is bid-endian or little
> endian?
>
Your experience differs from mine. There are lots of situations
where ASNs are discussed on telephone calls and/or transcribed
to/from yellow stickies, etc.

As to matching bits on the wire, no, it's not necessary, but, it is
a convenient side-effect.

>> 1. If you are a 16-bit AS speaker (ASN16), then AS65536 is not just
>>     the next one in the line, it is an AS that will have to be  
>> treated
>>     differently.  The code has to recognize it and replace it by the
>>     transistion mechanism AS.
>
> And how is a special notation superior to
>
>       if asnum > 65535 then
>           process_big_as
>       else
>           process_little_as
>
> In any case, people wishing to treat big asnums differently will need
> to write new code so the dot notation provides them zero benefit.
>
The dot notation is an improvement in human readability. It offers
no benefit to machines as they don't care as long as they have a good
parser for whatever notation is chosen.  The notation is for the human
interface.

> My point is that if we do NOT introduce a special notation
> for ASnums greater than 65536, then tools only need to be
> checked, not updated. If your tool was written by someone
> who left the company 7 years ago then you might want to
> do such checking by simply testing it with large as numbers,
> not by inspecting the code. The dot notation requires that
> somebody goes in and updates/fixes all these old tools.
>
So will the colon notation for IPv6 addresses.

Owen

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