[arin-ppml] Why are ISPs allowed?

Stephen Sprunk stephen at sprunk.org
Fri Jan 2 16:46:44 EST 2009

Artur (eBoundHost) wrote:
> My apologies if I'm asking a question that has been answered a million times, I have not been able to find an answer.
> Is there a reason why ISP's such as Comcast/ATT, allowed to hand out unique IP addresses, even not static ones, to end users?

Current policy says that assignments are justified if 25% of the space 
is used immediately and 50% of the space is used within one year.  It is 
reasonable to assume that each customer has at least one host 
(otherwise, why would they buy the service?) and thus assigning one 
address per customer is automatically justified.

> Why are they not required to use NAT?

NAT is generally considered "evil" and, so far, there is no consensus in 
the community that ISPs should be _required_ to use it.  It is an 
_optional_ technology that allows folks to use fewer addresses than 
would be justified.

> If ISPs were to switch to local address space, how many IP blocks would 
> be released back into the wild?

Most of them, I'd bet.

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