On Aug 6, 2011, at 3:15 AM, Jeff Wheeler wrote:
On Sat, Aug 6, 2011 at 5:21 AM, Owen DeLong <owen@delong.com> wrote:
At least don't make your life miserable by experimenting with too many different assignment sizes, or advocate /64s or something, that's considered a design fault which will come back to you some day. Read the RfCs and RIR policy discussions in the archives some years ago.
Note that in this thread, you advocate three things that are a little tough to make work together: * hierarchical addressing plan / routing * nibble-aligned addressing plan * minimum /48 per customer
Hasn't been hard so far.
If I were, for example, a hosting company with IPv6 terminated at the layer-3 ToR switch, I would then use a /40 per rack of typical "dedicated servers." If you then want some bits to be a POP-locator field for your hierarchical routing scheme, you are already forced to request more than a /32. The number of customers per layer-3 device for typical end-user access networks was around the same into the late-1990s/early-2000s, as ISPs had racks of Portmasters or whatever box of choice for terminating dial-up.
I think we were talking about access customers. I don't see giving /48s to individual dedicated servers as I don't see them having hierarchy behind them. I would think that a /48 per TOR switch would be reasonable in that case. However, requesting more than a /32 is perfectly reasonable. In the ARIN region, policy 2011-3.
Densities have changed, but this doesn't necessarily win you an advantage when combining those three properties. This is especially true if you consider that density may change in a difficult-to-predict manner in the future -- a BRAS box with a couple thousand customers today might have three times as many in a couple of years (IPv6 is supposed to help us avoid renumbering or injecting additional routes into our network, right?) As an access provider, if I shared your view, I would be reserving a /36 or /32 per BRAS box. If I then want some additional bits for hierarchical routing ... I'm going to need a pretty large address block for perhaps a pretty small number of customers. After all, my scheme, applying your logic, dictates that I should use a /32 or perhaps a /28 per each POP or city (I need to plan for several BRAS each), even if I don't have a lot of customers today!
Correct… I think a /36 per BRAS seems about right, but if you want to put more than 3072 customers on a single BRAS and expect technology to eventually support that, sure, go for a /32 per BRAS. If you want to isolate your routing down to per BRAS (most providers I'm aware of that have multiple BRAS have it set up so any customer in a given POP may connect to any BRAS and they carry the customer prefixes within the POP's routing table), then, I think a /36 per BRAS is probably OK (up to 3072 customers at 75% utilization, 4096 max), but, if you really think you will have 6,000 customer BRAS units, then, yes, a /32 would be correct. However, I would be more likely to assign hierarchy per POP instead. Figure out how many customers are likely in my largest POP and allocate based on /48 per customer+growth in that POP. For example, if my largest POP would serve 2,000 customer end-sites, I'd be looking at a /36 per POP. If the largest POP served 3,073 customer end-sites or even 49,000 customer end-sites, I'd plan on a /32 per POP. Basically take the number of customer end-sites in your largest POP, divide by 0.75 (keep 25% headroom minimum) and then round up to the nearest nibble. If you really think you will have more than 786,432 customer sites served from your largest POP, then, I suppose a /28 per POP is a reasonable request. That seems like pretty unlikely density, even in 20 years. I realize that customer density in urban areas does tend to increase, but, assuming a maximum 50% market penetration, serving a city the size of Philadelphia out of a single POP still seems unlikely to me.
I think /56 is more sensible than /48, given the above, for most end-users. Either way, the users will be gaining a lot more flexibility than they have with IPv4 today, where they probably get just one IP address and have to pay a fee for any extras. Giving the typical end-user 8 fewer bits worth of address space allows the ISP network more flexibility for hierarchical routing before they have to go to their RIR and figure out how to justify an out-sized allocation.
Why? You point out that giving out /48s would require larger IPv6 allocations than /32, but, you don't give any reason to think this is bad. Let's look at the math. Let's assume a moderately large provider expects to serve 45,000 customer end-sites out of their largest POP (does anyone actually expect numbers this large in a single POP)? Now, let's say you have 50 POPs across your service region and expect to triple in size over the next 5 years. That's 150 total POPs planned. 45,000 customer end sites with 25% minfree is 60,000 which, when rounded up to a nibble is 16 bits for 65,536. 150 POPs with 25% minfree is 200 which, when rounded up to a nibble is 8 bits for 256 total POPs possible. 16+8 = 24, so, such a provider would need a /24 for their access network. There are 512 /24s in each of the /12s (what the IANA issues to RIRs).
Also, if folks would stop thinking that every subnet should be a /64, they will see that end-users, makers of set-top-gateways, or whatever, can certainly address a whole lot of devices in a whole lot of subnets even if the user is only given a /64. Do we think DHCPv6 won't be the most common way of assigning addresses on SOHO LANs, and that SLAAC will be essential? I, for one, think that some ISPs will be sick and
Yes.
twisted enough to hand out /128s so they can continue charging for more IP addresses; but certainly the makers of IPv6-enabled devices will foresee that end-user LANs might not be /64 and include the necessary functionality to work correctly with smaller subnets.
I think natural selection in the market will solve that problem relatively quickly.
Before you beat me to it, yes, we seem to have completely opposing views on this subject. I will change my mind when I can go to the RIR and get a IPv6 /24 for a small ISP with a few POPs and a few tens of thousands of customers. Should RIR policy permit that sort of thing?
OK… Start changing your mind… Read 2011-3. It's been adopted in the ARIN region. I'd also like to suggest you consider supporting APNIC proposal 98 which is essentially the same policy and will be discussed at the Busan meeting. Owen