Network Administration

Dynamically assigning IPv6 addresses

In the previous chapter we had a look at how to dynamically assign IPv4 addresses and now let’s talk about dynamically assigning IPv6 addresses. With IP Version 6, we also need IP address information.

The length is the number of bits in the prefix, in the network portion of the address

 Just like IP Version 4, we have a prefix portion of the address that refers to the network portion and we’ve got a host portion of the address. But with IP Version 6, instead of having a subnet mask to say where we draw that dividing line, we have something called the prefix length. The length is the number of bits in the prefix, in the network portion of the address. 

And we also need information, such as, how do I get to a DNS Server so I can translate those names into IPv6 addresses? Now we certainly could do all of that manually and go in and one at a time add all this information to our clients, but a much more scalable solution is to use the DHCP Version 6 Server. 

Yeah, there’s a special version of the DHCP Server just for IP Version 6 clients. And there’s a couple of ways of doing this, Stateful and Stateless. First, consider Stateful DHCP Version 6. 

Dynamically assigning IPv6 addresses
Dynamically assigning IPv6 addresses

This works much like the IP Version 4 DHCP Server, where we learn all of our information from the server itself. Here, PCA says, “I need some IP address information.” And the DHCP Version 6 server gives it everything. It says, “Here’s your prefix, here’s your prefix length, “here’s your host information, “here’s the DNS Server’s IPv6 address.” We’ve learned everything from the DHCP Version 6 Server, but we don’t have to. Instead, we could use Stateless DHCP Version 6. 

With DHCP Version 6, the prefix and length information, we could dynamically learn that from our router using something called NDP or the Neighbor Discovery Protocol. What about the host portion of the address, though? Well, here’s a really cool trick that the PC can do. 

EUI-64 – Extended Unique Identifier

It can use something called EUI-64, that’s Extended Unique Identifier. And what that does, it takes the Mac address, that 48-bit address that was burned into the network interface card and it uses that as the basis of a 64-bit host address. So we’ve learned the prefix length portion of the address from the router, we’ve self-generated the host portion. 

Any extra information we might need though, yes, that could come from the DHCP Version 6 Server, such as the IPv6 address of a DNS Server. And that’s a look at how we can dynamically assign IPv6 information.

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