Categorie archieven: Netwerken

In this article, you will learn about the syntax of IPv6 site-local addresses and link-local addresses, which are so-called local-use, unicast addresses.

In the last post of this IPv6 tutorial, you learned about the different address types and the new public IP addresses, the global unicast addresses. Today I will introduce the so-called local-use, unicast addresses, which are those IPv6 addresses that are not routed across the public Internet. There are two types of local-use, unicast addresses: site-local addresses and link-local addresses.

Site-local addresses

Site-local addresses are equivalent to private IP addresses in IPv4. The address space reserved for these addresses, which are only routed within an organization and not on the public Internet, is 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. In IPv6, the first 10 bits of a site-local address are set to 1111111011, which is why these addresses always begin with FEC0. The following 54 bits are the subnet ID, which you can use in your organization for hierarchical routing, and the last 64 bits are the interface ID, which is the part that has to be unique on a link (local network on which hosts communicate without intervening routers). Thus, the prefix of a site-local address is FEC0::/10.

Link-local addresses

From IPv4, you might know APIPA (Automatic Private IP Addressing) or AutoNet. Whenever automatic IP configuration through DHCP fails, Windows automatically assigns an autoconfiguration address in the range 169.254.0.1 to 169.254.255.254, which allows the computer to communicate with other machines on the link. In IPv6, link-local addresses always begin with 1111111011 (FE80).

Unlike site-local addresses, link-local addresses are never forwarded by routers and therefore can only be reached on the link. This is the reason why the next 54 bits are set to 0. The last 64 bits are set randomly by the operating system.

There is an important difference between IPv6 link-local addresses and IPv4 APIPA addresses. Once a PC receives an IPv4 address from a DHCP server, the APIPA address is no longer reachable. However, with IPv6, a network interface always has a link-local address no matter if you assigned another IPv6 address manually or if the NIC received an IPv6 address from a DHCP server. This means that computers on a link can always communicate through IPv6 using link-local addresses, which is not the case in IPv4 because APIPA addresses are not in the same subnet as private or public IPv4 addresses. Thus, if the local DHCP is not available, the computers can still access local services through IPv6 but won’t be able to reach the Internet or services in other links.

In the next post of this IPv6 tutorial, I will talk a little about the zone ID and unique local IPv6 unicast addresses.

By Michael Pietroforte

[IPv6 – Part 1]  [IPv6 – Part 2]  [IPv6 – Part 3]  [IPv6 – Part 4]  [IPv6 – Part 5]  [IPv6 – Part 6]

This part of the IPv6 tutorial discusses the three general IPv6 address types (unicast, multicast, anycast) and introduces the sub type global unicast address.

In my last post in the IPv6 series, you learned the IPv6 address syntax. Today, I will introduce the different types of IPv6 addresses.

IPv6 address types

There are three general types of IPv6 addresses: unicast, multicast, and anycast.

Unicast addresses

You know unicast addresses from IPv4. A unicast address is the most common form of an IP address and is assigned to one network interface.

Multicast addresses

Multicast addresses are also known in IPv4. These addresses identify multiple network interfaces / hosts. A typical use of multicast addresses in a Windows environment is the deployment of OS images to multiple hosts, simultaneously.

Anycast addresses

This is a new address type in IPv6. Like a multicast address, an anycast address identifies multiple interfaces; however, while multicast packets are accepted by multiple machines, anycast packets are delivered only to one interface (host). This address type allows for services that are provided by multiple servers where only one server has to respond. In routing, anycast addresses are used to route packets to the closest routers.

And what about broadcast addresses? They no longer exist in IPv6. Broadcasts are replaced by multicast messages. I will say something about this IPv6 technique in a later post.

IPv6 knows five different unicast address types: global unicast addresses, link-local addresses, site-local addresses, unique local IPv6 unicast addresses, and special addresses.

Global unicast addresses

A global unicast address is simply what we call a public IP address in IPv4—that is, an IP address that is routed across the whole Internet. You can make out a global unicast address easily: The first three bits are set to 001. Thus, the address prefix of a global IPv6 address is 2000::/3 because 0010000000000000 is 2000 in hex. However, in the future, the IANA (Internet Assigned Numbers Authority) might delegate currently unassigned portions of the IPv6 address space. Hence, 2000::/3 won’t always be the prefix for global unicast addresses.

(Note: The diagram is from Microsoft’s “Introduction to IP Version 6.”)

The next 45 bits are the so-called global routing prefix. This is the part that is assigned to organizations. The following 16 bits are for the subnet ID, which you can use for hierarchical addressing in your network. The last 64 bits indicate the interface ID, which is the part of the IPv6 address that must be unique within a subnet. You know what this means, right? You can have 65,536 (=2¹⁶subnets), and each subnet can have 18446744073709551616 (=2⁶⁴) computers. I hope you have an efficient OS deployment tool.

In my next post, I will cover the site-local addresses and link-local address.

By Michael Pietroforte

[IPv6 – Part 1]  [IPv6 – Part 2]  [IPv6 – Part 3]  [IPv6 – Part 4]  [IPv6 – Part 5]  [IPv6 – Part 6]