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IPv6 Multicast and Anycast Addressing
(Page 4 of 5)
Solicited-Node Multicast Addresses
In addition to the regular multicast
addresses, each unicast address has a special multicast address called
its solicited-node address. This address is created through a
special mapping from the devices unicast address. Solicited-node
addresses are used by the IPv6
Neighbor Discovery (ND) protocol to provide
more
efficient address resolution than the
ARP technique used in IPv4.
All solicited-node addresses have
their T flag set to zero and a scope ID of 2, so they start with
FF02. The 112-bit group ID is broken down as follows (see
Figure 103):
Figure 103: IPv6 Solicited Node Address Calculation The solicited node multicast address is calculated from a unicast address by taking the last 24 bits of the address and prepending them with the IPv6 partial address FF02:0:0:0:0:1:FF. This shows the example address from Figure 95 converted to its solicited node address, FF02::1:FFC8:1FFF.
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- 80 bits consisting of 79 zeroes followed by a
single one; this means that in colon hexadecimal notation, the next
five hexadecimal values are 0000:0000:0000:0000:0001, or
more succinctly, 0:0:0:0:1.
- 8 ones: FF.
- 24 bits taken from the bottom 24 bits of its
unicast address.
So, these addresses start with FF02:0:0:0:0:1:FF
followed by the bottom 24 bits of the unicast address. So, the node
with IP address 805B:2D9D:DC28:0:0:FC57:D4C8:1FFF would have a solicited-node
address of FF02:0:0:0:0:1:FFC8:1FFF (or FF02::1:FFC8:1FFF).
Key Concept: Each unicast address has an equivalent solicited-node multicast address, which is created from the unicast address and used when other devices need to reach it on the local network. |
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Version 3.0 - Version Date: September 20, 2005
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