Now that IPv6 is imminent, you’ll need some IPv6 address space. Working with ARIN to request IPv6 differs from IPv4 procedures.
Now that IPv6 is imminent, you’ll need some IPv6 address space. Working with ARIN to request IPv6 differs from IPv4 procedures
Whenever I help a company deploy IPv6, the first question I’m asked is how to get provider independent IPv6 address space from ARIN. ARIN has new policy guidelines that affect how a company approaches its allocation justification request for IPv6 vs. what was required for IPv4.
First, I can’t emphasis enough how important it is for you to change your mindset when talking about IPv6 address requests. Remember, for the regional registry, IPv4 addresses are now a scarce resource and it has had policies in place for a while to conserve them. For IPv6 the whole process is turned on its head. The goal with IPv6 allocations is to give more than enough IPv6 address space. They want to prevent an organization from needing to come back to request more and also to avoid fragmented route prefix advertising in the core Internet routing tables.
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The quick and dirty for those that have an existing ASN and are BGP multi-homed network is that you automatically qualify for a /48 delegation from ARIN where a /48 is considered a single “site.” Translating that into number of subnets you have to build out as /64 networks is 64-48=16 which would be 2^16 or 65,536 subnets. Each subnet is a /64 which is 2^64 or 18,446,744,073,709,551,616 hosts.
Not bad but believe it or not there are a lot of use cases where even 18 quintillion IP addresses will not be enough depending on what your organization is providing in terms of services. To reduce the amount of work involved in justifying an allocation request, ARIN has made some simple breakdowns based on the number of sites an organization has or will have within the next 12 months. An initial size allocation will be based off the largest site you operate and the following:
- More than 1 but less than or equal to 12 sites justified, receives a /44 assignment
- More than 12 but less than or equal to 192 sites justified, receives a /40 assignment
- More than 192 but less than or equal to 3,072 sites justified, receives a /36 assignment
- More than 3,072 but less than or equal to 49,152 sites justified, receives a /32 assignment
If you have more than 49,152 sites you should look at ARIN’s ISP Address Space Guidelines, that will cover the allocation requirements for much larger organizations.
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As you can tell, it is pretty simple. You take the largest site you have and use that as the allocation basis. More than likely it fits within the /48 definitions. If so, then the allocation rules above (which allocate on natural nibble boundaries) are very generous. A nibble is four bits (i.e. one hexadecimal character) and in this case a natural subnet boundary is 4 bits, aka “nibble”, resulting in natural IPv6 subnets of /48, /52, /56, /60 and /64, for example. Keep in mind, the largest site you have dictates the use case so the reality is even if you have a smaller remote office with 12 folks they will get a /48 in this design. It allows you to grow that site to be identical to your largest current site topology.
The /40 allocation is really large. If you are at 16 sites, for example, you’ll end up with 256 sites (because of the round up to the next nibble boundary) with /48 address blocks each with 65,536 /64 subnets. That /40 is 16,777,216 /64 subnets for a single organization to operate and use. If your organization today is making use of RFC 1918 IPv4 address space, this allocation is identical in terms of the number of subnets in IPv6 vs. the total number of IPv4 addresses in RFC 1918 10.0.0.0/8.
Yes, I said you get as many subnets in a /40 delegation from ARIN as the total number of addresses you are used to using in RFC 1918 10.0.0.0/8 IPv4. That is an insane amount of address space!
By moving on a natural nibble boundary ARIN is being incredibly generous with IPv6 addresses but they are also simplifying the routing table by summarizing on easy subnet boundaries. They are gambling that the routing table summarization will pay off long term with service providers supporting end user delegations. This assumes that end users are not going crazy breaking up their subnet advertisements from their early initial allocations or at least doing them on even nibble boundaries. This shouldn’t be a huge issue since the majority of service providers will not accept IPv6 routes smaller than a /48 which corresponds nicely to the minimum provider independent block ARIN will give out being a /48 also.
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So, from the example above you can see that ARIN is doing the opposite of the sparse allocations traditionally done for IPv4. They are massively over allocating IPv6 address space in the hopes of not having to re-allocate address space and also simplifying the routing tables at the same time. Seems like a good plan out of the gate for now but I wonder if at some point it will be too generous and they will have to go back and modify the rules.
Horley is a principal solutions architect at Groupware Technology in the San Francisco Bay Area. Horley is actively involved in IPv6, serving as the co-chairman of the California IPv6 Task Force and being active with the North American IPv6 Task Force. Horley is a Microsoft MVP and has spent the last 15 years working in networking as an IT professional. He is involved in the Pacific IT Professionals Users Group, the largest IT pro user group in Northern California. Horley enjoys umpiring women’s lacrosse when he isn’t playing around on IPv6 networks. Contact him at ed@howfunky.com, @ehorley or check out his blog, HowFunky.com.
