This post is designed to give you a lot of information on implementing IPV6 into your network. Much of this has is aimed at the service provider market, but there are resources for the enterprise market.
One of the mindsets of this article is you are treating your customers as one of two ways. The first is a typical ISP end user. This can be John Smith on your wireless network or the small branch office down the street. These can vary in size and I will talk about how you can deal with these. The second type is the Enterprise or BGP peer. These are folks who should have their own IPV6 allocations and ASN.
Anyone who has followed me for a while knows I talk a lot of network philosophy. This article has bits of philosophy mixed in this article. Some of it is my own while others are the debates on certain aspects of IPV6 implementation. This is not a comprehensive guide to IPV6. rather, this is designed to fill in some blanks.
Packet Pushers has an excellent IPV6 planning podcast
Kevin Myers over at Stubarea51 has a great article on implementing IPV6 in a service provider market using Mikrotik
Typical service providers will are assigned a /36 or a /32 from their Regional Routing Registry (RIR). Don’t think in terms of IP addresses, but think in terms of subnets. I will emphasize this throughout the article. Also, another rule of thumb is when you are subnetting everything has to be done in multiples of 4 when it comes to the subnet mask. As with anything, there are exceptions but they might not be best practices.
IPV6 and Point-to-Point links
There is much debate on whether you should use a /64, a /124,126, or a /127 for point-to-point links. These would be the equivalent of /30’s in the IPV4 world. One of my favorite articles on this topic https://tools.ietf.org/id/draft-palet-v6ops-p2p-links-00.html
I typically use a /124 or /126, which seems to be what most of the larger upstream providers and content networks are using for point-to-point links. If you are using a /64 you have to contend with neighbor exhaustion attacks as well as ping pong attacks. One of the hybrid approaches is to use a /124,/126 or a /127 pulled from a single /64. I have yet to have a major upstream or content network hand me a /127.
Point-to-point links are one of the most highly talked about IPV6 methodologies. There are many right answers in this debate, as you can tell my the ietf article above. My advice is to pick one and go with it. The majority of the BGP peers I work with use either a /124 or a /126. I pull these out of a single /64. Some ISPs will allocate a /56 or /60, which we will talk about next, and use the first /64 and pull their point-to-point from that.
IPV6 and customer allocations
For years the standard allocation to a customer was a /56. In recent years this has been shrunk to a /60 with most of the major providers, such as Comcast. When we break down allocations in a service provider network, we have the standard accepted school of thought.
- Individual pops are assigned a /48 prefix.
- Enterprise customers are assigned a /56 prefix. That gives them 256 /64 subnets.
- Small customers are assigned a /60 prefix, allowing 16 /64 subnets.
One of the critical errors in thinking I see network engineers and architects do in IPV6 thinking is concentrating too much on IP addresses and not on the subnets. Just like in IPV4 subnetting it is all about the math. Assigning a customer a /64 directly is bad practice. The biggest reason is it does not allow the customer the ability to subnet the block into smaller chunks.
Some engineers think a customer will never use 18,446,744,073,709,551,616 and they would be correct. That is 18 quintillion IP addresses. 99.99 percent of us have never dealt with numbers that high. Many of us have only heard about numbers that high in science fiction such as Star Trek. However, a /64 is the smallest subnet assigned without breaking core functionality of IPV6. Remember earlier when we talked about point-to-point links? When we subnet out the /64 we are taking away sing a subnet prefix length other than a /64 will break many features of IPv6, amongst other things Neighbor Discovery (ND), Secure Neighborship Discovery (SEND) [RFC3971], privacy extensions [RFC4941], parts of Mobile IPv6 [RFC4866], PIM-SM with Embedded-RP [RFC3956], and SHIM6 [RFC5533]. Many new IPV6 developments also are relying on /64s being in place.
Back to our point-to-point addressing, we do not need neighbor discovery because we are only talking to one host. We don’t need privacy because we know the one host we are talking with, and so on.
But 18 quintillion IP addresses is still too much. Yes, but all the features relying on at least a /64 are worth the tradeoff. The key is to think in terms of subnets, not IP addresses.
So why not assign the customer a /62 to save on space..err..I mean subnets? Remember, when subnetting the math has to be in multiple of 4. So you can assign a /48, a /52, a /56, or a /60 to the customer and be safe. We talked about why assigning a /64 is bad practice even though it fits the multiple of 4.
Provider assigned IP (PI) space
There are very few cases for assigning Provider space to a customer who has an ASN. If the customer has an ASN they should be going to their Regional Internet Registry (RIR) and getting an allocation. In my case, most of the requests I do go through ARIN. Arin has a very good document on getting your first IPV6 allocation. https://www.arin.net/resources/guide/ipv6/first_request/
Anyone else I want to assign them a /56 or /60 as stated above. These are customer not participating in BGP. One of the lessons learned in the IPV4 world is how many started with provider assigned IP space and then went through the pain of renumbering when they received allocations from the RIR. In IPV6 we would have to re-subnet, but still the same pain.
What gets assigned IPV6 space?
One of my philosophies is I treat IPV6 like public IP addresses in the IPV4 world. I am not assigning Internet routable IP addresses to my switches, and APs unless they are doing routing. I can still use private Ip addresses for my infrastructure such as 10.x.x.x./8
Philosophies rounded up
-Point-to-point links. Should you use a /64,124,126,127, or even something else. I have seen Cogent hand me a /112 in several places
-Customer Allocations. Should you assign the customer a /56 or bigger? I believe any customer that needs more than a /56 should have their own ASN and their own IPV6 allocation. If necessary a large customer could have a /52 and still be within the bounds.
IPv6 is very much in flux with some conflicting methods of doing things. However, a good solid plan you stick to and follow can save you lots of headaches and allow your network to scale. Implementing IPV6 to some degree on your network should be a priority. There are many benefits to IPV6, which are not IP space-related which I will talk about in a later article
Other articles I have done on V6
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