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AVR2070
8240B-AVR-06/09
Any leading zeros can be dropped, writing addresses like:
2001:DB8:0:0:8:800:200C:417A
Finally a number of zeros in the middle of the address can be replaced with '::', as
such:
2001:DB8::8:800:200C:417A
All IPv6 networks have a “prefix” associated with them. Everything on the same
network has the same prefix, so for example the network might have the prefix
2001:0DB8:0000:0000::/64. The '/64' means the prefix is 64-bits long.
Here are a few important IPv6 prefixes that have been globally allocated:
::1/128 loopback address (note 128-bit prefix)
FF00::/8 multicast
FE80::/10 link-local unicast
Every interface always has a link-local address associated with it. The link-local
address is only valid on the network the device is on, it cannot be routed across
networks. This is important as the link-local address cannot be pinged across the
internet for example. The device needs to have a global address assigned to the
interface.
C.4.2 IPv6 Neighbor Discovery
IPv6 integrat
es into the core protocol how nodes find each other, their router, and
information about what network they are on. In IPv4 this was done with Address
Resolution Protocol (ARP) over Ethernet for example. This is required to find out the
mapping between a physical address and an IP address.
Neighbor discovery consists of four main types of packets. The first is neighbor
solicitation packets. These are sent to discover if a certain IP address is on the
same network, and if so what the physical address of it is.
A neighbor solicitation packet will be answered with a neighbor advertisement
packet. This advertises that a certain physical address is associated with an IP
address. Note the “physical address” will be referred to as the MAC, link-layer, Layer
2, or L2 address. All these terms are synonymous.
A node can send a router solicitation packet to inquire about routers that are on the
network like shown in Figure C-4-1.
A router solicitation is answered with a router advertisement packet. This informs
the nodes about the router information including: the physical address, router lifetime,
network prefix, and if the router should be used as a default router. This router
solicitation will also be periodically sent by the router to inform nodes of any changes
in network information.