Re: [Sip] Re: URI comparison rules - IPv6 addresses

[Paul Kyzivat <[e-mail]>]

[e-mail] wrote:
>    From: "Vijay K. Gurbani" <[e-mail]>
> 
>    Jeroen van Bemmel wrote:
>    > Vijay,
>    > It's not only IPv6: what about 127.0.0.1 versus 127.000.000.1?
> 
>    Jeroen: Pedantically speaking, you are probably right.  But
>    in practice we do not generally see leading zeros in an IPv4
>    octet.
> 
> Even worse, in some places, including some early RFCs, the leading
> zero is used to indicate that the octet is represented in octal!
> 
> But I think Jeroen's point is actually well-taken, when comparing
> representations of IP addresses (not DNS names), the comparison is
> implicitly of the address represented, not the textual
> representation.  And this applies in IPv4 as well as IPv6.
> 
> In regard to loop detection, there are two approaches:  (1) Whatever
> attempts to detect loops can canonicalize the addresses before
> comparing them or whatever. 

I agree with all the above.

> (2) Since there are a limited number of
> likely representations of any address, having different entities use
> different representations will only delay loop detection, not prevent
> it.  And loops will be detected even if address comparisons have
> occasional false negatives.

While the number is *limited*, the limit is pretty large.

Consider an IPv4 address where each of the components requires only two 
digits. Then each can be represented two ways - with two digits or 
three. That means there are 16 different valid representations of the 
address. Of course it would be much worse for Ipv6 addresses.

Port numbers are worse. The syntax for the port number is 1*DIGIT. So a 
port number can be represented with *any* number of leading zeros.

Bottom line - I think you can't rely on exhausting all the permutations 
of hostport before detecting a loop.

	Thanks,
	Paul


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