IPv6 eliminates the need for DHCP servers by using Stateless Address Autoconfiguration (SLAAC), a built-in mechanism that allows devices to generate and assign their own globally unique addresses. SLAAC is the preferred IPv6 address assignment method due to its simplicity, reduced infrastructure dependency, and lower configuration overhead.
IPv6 Address Assignment
As I mentioned in a prior video, when we came up with IPv6 we started recreating how this could function and what it can do, and one of the ideas behind this is we want devices to be self-sufficient and not have to rely on servers to get a bunch of information, where there are weak points. One of the ways that we've overcome this is that we've gotten rid of the DHCP server and have replaced it with SLAAC - stateless address autoconfiguration.
Let's do a little flashback to DHCP and figure out how IPv4 handed out its IP addresses. Then we can better understand some of the options that we have available with IPv6 and how we can hand out IPv6 addresses, or create IPv6 addresses.
DHCP is a protocol that's associated with IPv4. What it allowed was for a computer to attach to a network and then request - it would send out a broadcast and request an address - and then a DHCP server would then provide that address. It happened all on layer 2 as it was sent out, and it would be a broadcast. Well, that's not going to work with our IPv6, because we don't have broadcasts in IPv6.
So then we asked the question: how do we assign IPv6 addresses to machines?
First of all, we can just statically assign addresses to the machines. We just go on to the machine and statically configure the machine with an IPv6 address. You can imagine this can be very cumbersome. It was cumbersome even with IPv4 addresses, and now that you have such long addresses with IPv6 it would just become very hard to manage that.
We also then have stateful DHCP version 6. So this is DHCP version 6, which means that you have a server that can hand out IP addresses to your machines, and there's a mechanism that will allow this DHCP version 6 to work. We're not going to talk about it here.
Then we have SLAAC, and SLAAC is that automatic assignment of these.
We have already looked at how a machine can come up with the host bits - that's the link local address, or the interface side of the address - on its own, and verify that there's no other devices that are on this network that have that address, and therefore it would be a unique address on this network. If the network itself is a unique address and the address on this machine is unique within this network, then you know globally that this address is a unique address.
So really all it needs to be able to know is, on the network, what is the subnet, or what is the network address of this network right here. What it will do is it will do that router solicitation and ask the router for that information, and the router will then send back information about what network it's on. It takes that information about what network it's on and that unique address that it has for that network, it combines them together, and now it has a unique address out there in the world. That is how SLAAC works.
But it has a lot of options to it, and you can do a lot of configurations, things like DNS, and you can configure routers and default gateways. So there's a lot of configurations that you can have on there.
However, there are possibly situations where a DHCP server would actually serve that device better, and so in that case we can use both SLAAC and stateless DHCP. Stateful would mean that the DHCP server handled it all. Stateless DHCP means that this device actually gets most of its information from the router, but the pieces of information that it can't get, then it reaches out to the DHCP server. One of the pieces of information that this router would send back is: here is your information, but you will also need to reach out to the DHCP server to get some additional information.
So there you have it, it is the stateless address autoconfiguration. This stateless address autoconfiguration does just what we talked about, where a machine can take the information it gets back from the router to figure out the network portion of the address, and it has a mechanism to come up with the interface information, and combined, that will be enough information to get out to the real world.
This is the preferred method because it doesn't rely on any single piece of equipment that's out there. There's very little configuration that happens with this. What we call this is a stateless, where it is just self-serve, and so these devices can serve themselves. They just need that little piece of information and then they come up with those addresses. That's why it's stateless.
IPv6 does have a DHCP version 6 option, where you can use a DHCP server, but that is not the preferred method. The preferred method is to use this stateless address autoconfiguration, because that process is already built into IPv6, it's really simple to set up, it is less reliant on other equipment to make sure that things are connected correctly, there are less configurations, and there are less chances of things going wrong. So SLAAC really is the preferred method for setting up your devices with IPv6 addresses.
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