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8240B-AVR-06/09
Figure C-4-1 IPv6 Router Discovery
C.4.3 Node Auto-configuration
On po
wer-up a node uses these packets to acquire an address using stateless auto-
configuration. It first auto-configures a link-local address by using the fe80:: prefix
followed by an interface identifier description (IID) based on its physical address. It
then sends a neighbor solicitation packet looking for someone else with this same
address – this is the duplicate address detection (DAD) phase. If no response is
heard to the neighbor solicitation, it assumes it has a valid unique address. A router
solicitation is then sent out to learn about any on-link routers. If the routers have prefix
information, it can then combine the network prefix with the IID to form a globally
accessible address.
As an example, consider how an Ethernet interface with a physical address of
00:1C:23:2B:BD:6C gets a fully operational address:
1. Node comes to life, calculates an IID of 021c:23ff:fe2b:bd6c/64 from its
physical address.
2. Node sends a neighbor solicitation to fe80::21c:23ff:fe2b:bd6c.
3. Node waits for response, resending neighbor solicitation a certain number of
times.
4. Node fails to hear a response, so auto-configures itself to have the address
fe80::21c:23ff:fe2b:bd6c.
5. Node sends a neighbor advertisement, advertising it has address
fe80::21c:23ff:fe2b:bd6c.
6. Node sends a router solicitation.
7. Router sends a router advertisement, out of which node finds the network
prefix is 2001:db8:1e1::/64.
8. Node sends neighbor solicitation to 2001:db8:1e1:0:21c:23ff:fe2b:bd6c, again
listening for a response.
9. No response heard, node advertises itself as owning address
2001:db8:1e1:0:21c:23ff:fe2b:bd6c.