Slaac vs DHCPv6

Slaac vs DHCPv6

In this section, the functionality of SLAAC VS DHCPv6 is explored . Also the options of obtaining an IPv6 address automatically.Similar to what happens with IPv4, global unicast IPv6 addresses can be configured manually or dynamically. However, there are two methods in which IPv6 global unicast addresses can be dynamically assigned:

• Automatic stateless address configuration (SLAAC)
• Dynamic host configuration protocol for IPv6 (DHCPv6 with status)

What is SLAAC ipv6

SLAAC (Automatic state independent address configuration) is a method in which a device can obtain a global unicast IPv6 address without the services of a DHCPv6 server. ICMPv6 is located in the center of SLAAC. ICMPv6 is similar to ICMPv4, but includes additional functionality and is a much stronger protocol. SLAAC uses ICMPv6 router request and announcement messages to provide addressing and other configuration information that would normally be provided by a DHCP server:

1. Router request message (RS): When a client is configured to obtain the routing information automatically via SLAAC, the client sends an RS message to the router. The RS message is sent to the IPv6 multicast address of all routers, FF02 :: 2.
2. Router Announcement (RA) Message:  Routers send RA messages to provide routing information to clients configured to obtain their IPv6 addresses automatically. The RA message includes the prefix and prefix length of the local segment. A client uses this information to create its own global unicast IPv6 address. Routers send RA messages periodically or in response to an RS message. By default, Cisco routers send RA messages every 200 seconds. RA messages are always sent to the IPv6 multicast address of all nodes, FF02 :: 1.

As the name implies, SLAAC means "stateless." A stateless service means that there is no server that maintains the network address information. Unlike DHCP, there is no SLAAC server that has information about which IPv6 addresses are in use and which ones are available.

Operation of SLAAC

A router must have IPv6 routing enabled before it can send RA messages:

Router (config) # ipv6 unicast-routing

SLAAC VS DHCPV6

The decision of whether a client is configured to obtain its IPv6 address information automatically via SLAAC, by DHCPv6 or by a combination of both depends on the configuration within the RA message.

The two indicators are the managed address configuration indicator (M indicator) and the other configuration indicator (O indicator).

Using different combinations of the M and O indicators, RA messages have one of three addressing options for the IPv6 device, as shown in the illustration:

• SLAAC (router ad only)
• Stateless DHCPv6 (router and DHCPv6 announcement)
• DHCPv6 with status (DHCPv6 only)

Regardless of the option used, in RFC 4861 it is recommended that all IPv6 devices perform duplicate address detection (DAD) at any unicast address, including addresses configured using SLAAC or DHCPv6. DAD is implemented by ICMPv6, specified by RFC 4443.