[arin-ppml] Clarification on "a block designated for that purpose"

michael.dillon at bt.com michael.dillon at bt.com
Thu Feb 25 04:04:41 EST 2010

> When I came up with 'a block designated/reserved for that 
> purpose', I was not attempting to segregate the IP space into 
> another classful environment.

Why not? Classes are good. Classes simplify things. That is
why the designers of IPv6 use a loosely classful model.
People are under the mistaken impression that classful
networking is bade because of the history of IPv4. But
IPv4 classes were not bad, they were too small and too
rigid. In IPv6, the classes are much larger and very
unlikely to be too small. And in IPv6 we have only
designated about 1/8th of the space so there is even
room for additional classes so we don't have the 
rigidity problem.

Note that IPv4 today is still classful. We don't have 
Class A, B and C any more, but we still have class D
multicast and RFC 1918, and a few other special use

It is a GOOD thing if ARIN applies classful thinking
and uses a designated block for address allocations
which providers will likely want to treat AS A CLASS
and apply the same policy towards them. 

> - it's an ARIN allocation, and it falls within the 'special IX' space
> - we weight the traffic differently, and allow it for an 
> extended period

That is a class of address. If the special IX space was
a list of 379 scattered allocations ranging from /24 to
/19, you would do more work than if it was all from a
single ARIN /15 block. The CLASS exists regardless of
whether ARIN does the sensible thing or not.

> - whether custom or [insert very expensive network] software, 
> if the space is going to be segregated in ANY regard, it is 
> in the best interest of the entire community to be able to 
> have a safe understanding of the identity of what that IP 
> address is, and what its purpose is.

Indeed. Network operators do CLASSify addresses and apply
special behaviors according to the CLASS. Since ARIN
serves the community, ARIN should model allocations according
the the CLASSful activities of operators, where that is

> My point is, is that having ALL IP space alloc'd/assigned out 
> of blocks reserved for that purpose is for `informational purposes'.

Yes, for CLASSification purposes.

> I'm not trying to imply a new classful strategy.

Of course not. The classful strategy already exists and was
implemented by network operators. ARIN is simply coming into
alignment with what network operators already do because it
it benefits the network.

> There are no restrictions. Again... I'm not asking for ARIN 
> to create a "boundary" here.

Sure you are. Otherwise you would ignore this issue entirely
and work with someone like Cymru to set up a registry to
track all the special case blocks.

> As an engineer/operator, I just 
> would find it easier that if the IP space was to be 
> segregated, that it be segregated in a way that it be 
> documented publicly, so that ops *could* make 
> routing/forwarding decisions on the documentation if they *chose* to.

I agree with you that this is a good thing.
Classes are good, and subclasses like this are within the
scope of ARIN's charter. We may not determine network operations
activity, but we have always tried to fit in with it as
long as it was consistent with the public interest.

When ARIN started, network operators used classful filtering
on incoming BGP announcements since they knew that ARIN's minimum
ISP allocation on certain /8s, was /19. ARIN had defined the class
and operators leveraged that information. 

--Michael Dillon

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