DHCPv6 Overview


Dynamic Host Configuration Protocol version 6

IP Allocation can be done with different mechanims in IPv6. Mainly, we can devide IPv6 Allocation mechanims into two. These are:

• Manual
• Dynamic

Manual IP allocation is the way that network engineers manually assign IPv6 addresses.

Dynamic IP Allocation is the way, that different mechanims are used for automatic IP allocation. Dynamic IP Allocation is mainly divided into two according to their operational style. These are:

• Stateless IP Allocation
• Stateful IP Allocation

Stateless IP Allocation is done with SLAAC (Stateless Auto Address Configuration). This mechanims is also explained in another lessons.

Stateful IP Allocation is done with DHCPv6. In this article, we will focus mainly DHCPv6.

DHCPv6 Messages

Dynamic addressing starts with IPv6 Router Advertisement (RA) Messages.The aim of these messages is, informing the network devices about how they can reach IPv6 addressing Information.

Router Advertisement (RA) Messages are sent periodically or any time after receiving a Solicitation Message.
With this Router Advertisement Messages, router answers in four ways:

1) SLAAC (Cisco Default, Stateless)
2) SLAAC + DHCPv6 (Stateless)
3) DHCPv6 Offer (Statefull)
4) DHCPv6 Offer (Statefull + Stateless)


Router Advertisement Flags

There are three important flags in a Router Advertisement Message, to use DHCPv6 or not. These flags are:

• Other Configuration Flag (O Flag)
• Managed Configuration Flag (M Flag)
• Auto Configuration Flag (A Flag)

“O” flag indicates that, Stateless Auto Configuration will be done or not. If it is set to 1, Statefull configuration can also be done. “M” flag indicates that Auto IP Configuration will be done with DHCPv6 or Not. If it is set to 1, then Auto IP Configuration is done by DHCPv6. The other important flag is “A” Flag. If it is 1, auto stateless configuration is done if 0 then stateful DHCP is used.

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