IPv6 address assignment
With IPv4, one would assign addresess in one of the three following ways:
- Via DHCP (Dynamic Host Configuration Protocol)
- By manually assigning the addresses
- Using APIPA (Automatic Private IP Assignment)
With IPv6, these three ways are still available, although we refer to the third as stateless address autoconfiguration or SLAAC (which also makes this one of the best acronyms in computer history alongside FAQ and SCSI). SLAAC is used when the system assigns itself the link-local address (the one starting with FE80) that we discussed earlier.
The reality is that most administrators deploying Unified Remote Access (URA) will want to know as little about IPv6 as possible, and would rather not have to even think about messing around with DHCP scopes or subnetting. As luck would have it, you don't really have to, because the fantastic ISATAP mechanism will help you work things out. ISATAP (Intra-Site Automatic Tunnel Addressing Protocol) is a protocol transition mechanism, which provides a way for computers to communicate, using IPv6 over an IPv4 network, and part of that is an automatic generation of an IPv6 address. The way this works is by Windows creating a virtual network card named isatap, and assigning itself an IPv6 address that's based on the computer's IPv4 address. This would happen on all your modern desktops and servers (Windows XP, Windows Vista, Windows 7, Windows Mobile, Windows Phone 7, Linux, and even some versions of Cisco IOS). A computer or network device on your network will be designated as an ISATAP Router (more about that later) and your hosts will learn of its existence by querying your DNS server.
As you can see in the following screenshot, this computer assigned itself the ISATAP address of 2002:2f6b:1:1:0:5efe:10.0.0.3. Did you see those dots at the end? Yes! This shows us that the address was generated from the computer's IPv4 address of 10.0.0.3. Easy as pie!
If you prefer, you can ask your ISP to assign you an IPv6 subnet, and then create a DHCP scope from it to assign real addresses, and you could even assign those addresses manually to hosts. You can also work with your ISP to devise an IPv6 address allocation plan, if your network is complex.
We'll say this again, though you don't have to do any of this for the purpose of implementing URA. The reason for this is even though URA clients do use IPv6, the URA server will actually route that traffic and encapsulate it as IPv4 to the hosts on the corporate network. We will discuss this in more detail shortly.