[ppml] Proposed Policy: Adding an HD ratio choice for new IPv4 allocations

[Charles Scott]

Michael:
  You seem to be supporting my point, that, if anything, HD ratio applies 
to end-user address utilization, for which there is already significant 
accommodation for these issues as your examples would easily be 
accommodated by the 25%/50% policy for end-user address utilization. 
  Is there something else I'm missing?

Chuck Scott
cscott at gaslightmedia.com



On Tue, 22 Feb 2005 Michael.Dillon at radianz.com wrote:

> > >  When this last came up I questioned why HD Ratio should be applied to
> > >ISP allocations/assignments and received no responses. In fact, I even
> > >challenged the application of HD Ratio to end-user address space on the
> > >premise that the argument for HD Radio is based on the need to 
> implement
> > >a strict hierarchical numbering scheme. With dynamic routing protocols 
> it
> > >is not necessary to have a network hierarchically arranged strictly by
> > >numeric address--subnets can appear in networks to which they are not
> > >numerically related. 
> 
> To begin with, it's not hierarchy alone that creates the
> problem. Hierarchy interacts with the bit-mask operations
> used to divide network addresses and host addresses. These
> bit-mask operations impose a power-of-2 structure on network
> sizes and aggregate sizes. The hierarchy exacerbates the
> problem because the power-of-2 rule applies at each level.
> 
> Suppose that I have a special product that requires 5
> IP addresses per customer. I have 5 PoPs with 25 customers
> at each PoP. Therefore, at each PoP I need 125 addresses for
> a sum total of 625 addresses to cover the needs of all 
> 5 cities.
> 
> But IPv4 doesn't work that way. In fact, I have to give each
> customer 8 addresses for a total of 200 addresses at a PoP.
> That makes 1000 addresses in total, right? Wrong. I have to 
> give each PoP 256 addresses, not 200. That makes for a total
> of 1280 addresses. This is how hierarchy increases inefficiency
> by compounding the "overhead" associated with the power-of-2
> rule.
> 
> In a real network, each of the subnets will also have extra
> addresses to accomodate growth because no network operator
> can function by only growing their subnets by one customer
> requirement at a time. The larger the network, the more this
> overhead eats up addresses especially when you are trying 
> to make sure that routes can be aggregated to keep the number
> of individual routes low. In a small network you can ignore 
> aggregation, give every customer a random block of addresses
> and let dynamic routing sort out the mess. This will not
> scale.
> 
> --Michael Dillon
> 
>