In order for the datagrams in their header to make the basic specification of the initial and destination addresses, they must first be assigned to the network subscribers. They are usually assigned between internal and external, or public IP addresses. Three address ranges are reserved for the former, which are used for communication in local networks:
- 10.0.0.0 bis 10.255.255.255
- 172.16.0.0 bis 172.31.255.255
- 192.168.0.0 bis 192.168.255.255
The prefix “fc00::/7” is provided for IPv6 networks. Addresses in these networks are not routed in the internet and can therefore be freely selected and used in private or company networks. Addresses are successfully assigned either by manual input or automatically as soon as the device connects to the network, as long as the automatic address assignment is activated and a DHCP server is in use. With the help of a subnet mask, this type of local network can also be selectively segmented into other areas.
External IP addresses are routed automatically by the respective internet provider when they connect to the internet. All devices on the internet via a common router access the same external IP. Typically, the providers assign a new internet address every 24 hours from an address range, which was assigned to them by the IANA. This also applies to the almost inexhaustible arsenal of IPv6 addresses, which are only partly released for normal use. Furthermore, it is not just divided into private and public addresses, but it can be distinguished by much more versatile classification possibilities in so-called “address scopes”:
- Host Scope: The loopback address 0:0:0:0:0:0:0: can use a host to send IPv6 datagrams to itself.
- Link Local Scope: For IPv6 connectivity, is it essential that each host has its own address, even if it is only valid on a local network. This link local address is identified by the prefix ”fe80::/10“ and is used for example, for communication with the standard gateway (router) in order to generate a public IP address.
- Unique Local Scope: This is the aforementioned address range “fc00::/7”, which is exclusively reserved for the configuration of local networks.
- Site Local Scope: The site local scope is an now outdated prefix “fec0::/10”, which was also defined for local networks. However, as soon as different networks were connected or VPN connections were made between networks that were numbered with site-local addresses, the standard was considered overtaken.
- Global Scope: Any host that wants to connect to the internet at least needs its own public address. This is obtained by auto-configuration, either by accessing the SLAAC (stateless address configuration) or DHCPv6 (state-oriented address configuration).
- Multicast Scope: Network nodes, routers, servers and other network services can be grouped into multicast groups using IPv6. Each of these groups has its own address, which allows a single packet to reach all the hosts involved. The prefix “ff00::/8“ indicates that a multicast address follows.