Stateless autoconfiguration for IPv6

Can you explain what is ND and NDp in the routing table?

Hello Giovanni

When you configure stateless autoconfiguration for IPv6, these entries are automatically created within the IPv6 routing table.

Which ones are installed depends upon the specific autoconfiguration setup. When the following command is implemented, only the NDp entry appears.

ipv6 add autoconfig

The ND entry has the IPv6 address of the router from which the IPv6 address was obtained. Now if the following command is used, then the ND entry appears as well:

ipv6 add autoconfig default

More info can be found at this Cisco Learning Network post:

I hope this has been helpful!


In this example, how does R2 know to send an RA message to R1?


Given this is not sent as a broadcast, what dest mac address would be used by R2?

NDP requires a IP address for the process so that’s not going to work here.
There is no more broadcast address or limited broadcast here, either.
so its likely a multicast address, which leads to a question when autoconfigure is used, dose it listens for a specific multicast mac address?



Hello Patrick

Actually, when the ipv6 address autoconfig command is applied to Fa0/0 of R1, it sends out a Router Solicitation (RS) message. This was not shown in the debug because it was enabled after the autoconfig was configured on R1. R2 sends an RA as a response to the RS.

Let’s take a look at a Wireshark capture of an RA. This is takeen from this Cloudshark capture.

Notice the MAC address of 33:33:00:00:00:01 as the destination address. How is this determined? Well, IPv6 multicast uses the prefix 33:33:xx for IPv6 multicast traffic. To determine the multicast MAC address, you take the initial multicast IPv6 address of ff02::1 which is the all nodes on the local network segment, and OR it with the MAC address of 33:33:00:00:00:00. The result is 33:33:00:00:00:01.

More about this can be found in RFC 2464.

I hope this has been helpful!