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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:

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

wdavis84 says:

Hi Rene,

Do you have lesson configure the RA preferences? More on how the LAN host get the DHCPV6 address and which router will be the elect as default gateway.

And the show ipv6 router command is something like show arp in IPV4?

Davis
caspervisser says:

Hi Davis

I know it’s a bit of a late response but just to add onto this. On the client you can also add the syntax “default” after the statement “ipv6 address autoconfig”

e.g. “ipv6 address autoconfig default”. This will inject a default route on your client.
mr_nasser1980 says:

please check:-
“The big difference between DHCP for IPv6 and DHCPv6 is that we don’t use broadcast traffic anymore”

I think you mean DHCP for IPv4
ReneMolenaar says:

Hi Nassir,

That’s correct, thanks for letting me know. Just fixed it.

Rene
lagapides says:

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
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