Neighbor solicitation messages are used for autoconfiguration of IPv6 addresses and detecting duplicate addresses on the local network. When a node needs to autoconfigure an IPv6 address, it sends a neighbor solicitation with an unspecified source address and the potential target address in the message. This allows the node to determine if any other nodes are already using that address. Responses from other nodes help identify duplicate addresses before finalizing the new address. Neighbor solicitation thus plays a key role in automatically assigning unique IPv6 addresses during configuration.

1. IPv6 headers, Neighbor
solicitation, and Router Advt
(Part 2)
By: Indraneel Pole

2. • My idea of neighbor solicitation was that it solicitates the neighbors
by sending this request.
• This is largely true. But not the only thing what neighbor solicitation is
supposed to do.
• This week I will talk about Neighbor solicitation and how it can be
used for autoconfiguration of IP addresses.
Neighbor Solicitation

3. Neighbor Solicitation
• Here is what RFC has to say about Neighbor solicitation

4. Autoconfiguration of IPv6 address and
Neighbor solicitation
• The very crucial information that neighbor solicitation is also used for
detection of duplicate addressing leads to a different direction for
address autoconfiguration
• Consider a scenario where a node has to autoconfigure IPv6 address
for its own. How does it come to know that the address it is taken for
itself is not already taken by any other node in the same network. (Of
course autoconfig of IPv6 is done by converting MAC address to EUI -
64 format and so on, and of course MAC address is unique to device,
but it can be modified, as some of you geeks might know)

5. • Naturally the mentioned scenario would require the node to search
for a duplicate address in the existing network. And that exactly is
what neighbor solution is also suppose to do.
Autoconfiguration of IPv6 address and
Neighbor solicitation

6. Finding duplicate Addresses
• Once again here is the snippet of Wireshark frame

7. As you see the snippet, you figure out two-three things –
1. Source Address – this is usually address of node which sends solicitation
request, but as this node is doing the solicitation in order to configure an
IP address for itself, the „src“ field is unspecified.
2. The destination address is a multicast address which actually
corrosponds to target address. This specifies that this is the multicast
group which node wants to join.
3. And most importantly, „Target Address“. This is usually the address of the
solicitation as the RFC states. But as in this case the node is trying to find
the duplicate node, this is the address which actually our node wants to
take.

8. End of Part 2
• So as you can see neighbor solicitation by a node also plays a crucial
role in finding the IPv6 address for the node itself.
• If you see such capture, first look at the „src“ field, and if it is
unspecified, the target address is the IPv6 address of your node.