1 IPv6 address format
94 Chapter 4
it is assigned to many nodes. The closest node to the originator is where the message
is routed to, using rules within the routers to determine distance. When a device needs
to connect into an IMS, it can use an Anycast address and be connected to the closest
P-CSCF, without having to know the address of that individual P-CSCF, and without
having to query another server for the address.
Using Anycast addressing at the CSCF level will certainly eliminate the maintenance
of addressing within the network. There may be some security concerns using
Anycast addressing, since there is only one address to learn to gain access anyplace in
the network, but this can easily be resolved through other security measures as discussed
in Chapter 6.
A multicast address is much like a broadcast address (see Figure 4.2). In fact, multicast
has replaced the broadcast addresses used in IPv4. With a multicast address,
multiple nodes are reached using the same address. Of course, the address is formatted
in such a way that all receiving nodes understand that they are receiving a message
sent to a multicast address.
Multicast addresses can be used to send communications to all subscribers within an
operator??™s network, for example. Use of this form of address provides an easy method
for reaching a broad range of users or devices without the assignment and creation of
distribution lists.
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