64 AVR2070 8240B-AVR-06/09
Compared to normal IPv6 networks, there are some differences to how a node
acquires its IPv6 address. A typical startup sequence on this Atmel 6LoWPAN
network is (shown in Figure C-4-1):
1. Node associates to coordinator using RUM protocol, and is assigned an
802.15.4 short address
2. Node sends IPv6 router solicitation to edge router (coordinator)
3. Edge router sends router advertisement back, including IPv6 prefix
4. Node stores this prefix as the default context it uses in all communication
5. Node now has an IPv6 address, since it has context and a short address
There are several differences from the normal IPv6 auto-configuration. Sending
physically multicast / broadcast messages is eliminated, as it is not necessary since
the edge router address is already known from RUM association. End nodes do not
perform duplicate address detection, as each node is guaranteed to have a unique
address on the 6LoWPAN network.
The current IPv6 stack on the end devices (AVR) has some limitations. The most
important ones are:
• Incoming IPv6 checksums are not checked, however outgoing packets have
valid checksums in them.
• The IPv6 edge router and PAN coordinator must be the same device.
• Fragmentation is not provided at the 6LoWPAN layer, meaning packets must
fit within a single 802.15.4 frame.
• All IPv6 addresses of nodes on the network must be based on short
addresses.