Network Basics: Assigning IPv6 Addresses
By Edward Tetz
If you're working in a Cisco network and assigning addresses to your IPv6 network cards,
you need to know that just like IPv4 addresses there is a network portion of the address and
a host portion of the address.
Both portions are 64-bits long, so the first 64-bits of an IPv6 address is the network
address (sometimes referred to as a network ID or network prefix), and the last 64-bits of
an IPv6 address is a unique host ID for the specific network ID. The four methods of assigning
IPv6 addresses are:
• Manual Interface ID Assignment: An address is manually assigned to an interface.
This is fairly easy to do with most Cisco devices from the interface configuration with a command like
Router1(config-if)# ipv6 address 2001:DB8:1111:2222::54/64
As with any manual system, it is easy to assign one address to one interface; but you
may not want to manually assign addresses to every device on your network manually.
• EUI-64 Interface ID Assignment: This is similar to a full manual address,
but instead of specifying full address, you configure only the network portion of the address,
and the remainder of the address is derived from the interface’s Media Access Control (MAC)
address. When configuring this from the interface prompt, the command looks like this:
Router1(config-if)# ipv6 address 2001:DB8:1111:2222::/64 eui-64
The MAC address on your network interface is a 48-bit number and may sometimes be referenced
as MAC-48 to denote the length. Because the MAC address is a unique identifier, it can also
be referred to as an Extended Unique Identifier (EUI) of 48-bits or EUI-48. MAC refers to a
network interface identifier, whereas EUI-48 could be assigned to other devices.
The MAC address on your network interface is a 48-bit number and may sometimes be re
When designing IPv6, the designers wanted to have unique identifiers that were larger than
the current EUI-48, so they lengthened the identifier to 64-bit and created the EUI-64 identifier.
So an EUI-64 is simply a globally unique identifier.
This configuration makes address assignment much easier because all devices on the same
data link share the same network ID, and all you need to have automatically assigned is the
host ID, which is guaranteed unique because it is based on the already globally unique MAC address.
• Stateless Auto-Configuration: This is by far the easiest way to configure
an IP address on an interface, allowing full automatic configuration. This configuration mode
was created to allow all devices on the same data link to automatically configure themselves,
reducing administrative overhead for the network administrators. In addition to full auto-configuration,
Stateless Auto-Configuration sends a request for a router advertisement (RA), which is used
by the client as a 64-bit network ID prefix to the client’s IP address.
The MAC address on your network interface is a 48-bit number and may sometimes be re
This means that if you have configured your routers with their 64-bit network IDs, your network
devices use those network IDs; otherwise, all your network IDs for your internal network are
assigned automatically. The 64-bit network ID could be a global or private address, but the
remaining 64 bits of the address are chosen automatically by the client.
• DHCPv6 (Stateful): Dynamic Host Configuration Protocol (DHCP) servers that
have the appropriate extensions installed for IPv6 can process DHCP address requests. This
process for handing out addresses is similar to IPv4; the server is configured with an address
pool to hand out, and it randomly fills the address requests from this pool. This process allows
for complete control over the assigned client IP address, as well as being able to view the
list of assigned addresses.
The MAC address on your network interface is a 48-bit number and may sometimes be re
In DHCPv6, the client first checks for a router advertisement; and if there is, the client
is allowed to use DHCP. If there is no router or the router allows for DCHP, the client sends
a multicast request to all DHCP agents on the network; if there are no router advertisements
or DHCP responses, the client uses the local-link address.
This is an excerpt from:
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