Stateless autoconfiguration for IPv6

Stateless autoconfiguration for IPv6 is like a “mini-DHCP” server for IPv6. Routers running IPv6 can give the prefix of the network and a gateway address to clients looking for an IPv6 address. IPv6 uses the NDP (Neighbor Discovery Protocol) and one of the things this protocol offers is RS (Route Solicitation and (RA) Router Advertisement messages that help an IPv6 device to automatically configure an IPv6 address. Let’s take a look at a configuration example:

two routers running ipv6
I’m going to use two routers to show you how stateless autoconfiguration works. R2 will have an IPv6 address and is going to send router advertisements. R1 will use this to configure it’s own IPv6 address.

R2(config)#ipv6 unicast-routing 
R2(config)#interface fastEthernet 0/0
R2(config-if)#ipv6 address 2001:1234::/64 eui-64

Besides configuring an IPv6 address we have to use the ipv6 unicast-routing command to make R2 act like a router. Remember this command since you need it for routing protocols as well.

R1(config)#interface fastEthernet 0/0
R1(config-if)#ipv6 address autoconfig

We need to enable ipv6 address autoconfig on R1 to make sure it generates its own IPv6 address.

R1#debug ipv6 nd 
ICMP Neighbor Discovery events debugging is on
R2#debug ipv6 nd 
ICMP Neighbor Discovery events debugging is on

We can use debug ipv6 nd to watch the whole process.

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Forum Replies

  1. Hello Hugues

    When using SLAAC, the addresses that are configured depend on the operating system being used. Specifically for Cisco IOS devices, the EUI64 process is used by default. This means that the actual IPv6 address that a Cisco device will obtain will depend directly on the MAC address of the device itself. If this device is then removed and another device is put in its place, because MAC addresses are unique, the new IPv6 address it will obtain will be different. If the same device is shutdown and restarted, then the same IPv6 address will be assign

    ... Continue reading in our forum

  2. Thanks Laz - your comprehensive answer is much appreciated! :):smile:

  3. Hello Marit

    The ipv6 unicast-routing command enables the router to route IPv6 packets. This essentially allows a router to create an IPv6 routing table, and to be able to respond to Route Solicitation messages with Router Advertisement messages. This command does not affect the ability of specific interfaces to function as IPv6-addressed hosts. You can have IPv6 enabled interfaces without enabling IPv6 routing. These interfaces would simply function as IPv6 hosts that can send and receive IPv6 packets, but the router will not be able to forward any such pac

    ... Continue reading in our forum

  4. As usual a crystal clear answer, thanks Laz!

  5. Hi,

    Thanks for the clarification. It did occur to me it might use all of them because IPv6 isn’t like IPv4 in the way that additional addresses are secondary.

    Thanks again.


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