 be nonsensical, but you'll see it a lot in IPv6. Where IPv6 differs is the way that addresses are with regard to considering network masks. With IPv4 and CIDR, there are no classes, SO almost any number of bits can be used in the network mask. With IPv6, there are more defined rules: Network address range The first 48 bits of IPv6 addresses are reserved for Internet routing: ffff:ffff:ffff:0000:0000:0000:0000:0000 Subnetting range The 16 bits from bit number 49 to bit number 54 are for defining subnets: (0000:0000:0000:ffff:0000:0000:0000:0000 Device range The last 64 bits are for device addresses: (0000:0000:0000:0000:ffff:ffff:ffff:ffff You can use a portion of the device address to further refine a subnet, but it is not recommended. You'll see why in a bit. Address Types Like IPv4, certain addresses are special and are identified by their high-order bits. These address types are identified in RFC 4291 (section 2.4) and are given in Table 37-1. Table 37-1. IPv6 address types Address type Binary prefix IPv6 notation Section Unspecified 00...0 (128 bits) ::/128 2.5.2 Loopback 00...1 (128 bits) ::1/128 2.5.3 Multicast 11111111 FF00::/8 Link-local unicast 1111111010 FE80::/10 2.5.6 Global unicast (everything else) Unspecified address An unspecified address is an address of all zeros. Packets with an unspecified des- tination will be dropped by routers. The source address may be unspecified by devices that have yet to learn their address. Addressing Loopback address The loopback address in IPv6 is 0:0:0:0:0:0:0:1 or :1/128. This is analogous to 127.0.0.1 in IPv4. Be careful of your subnet masks. /32 in IPv4 indicates an all-ones mask or a specific host address. /32 in IPv6 means something en- tirely different, namely a very large-scale aggregate Internet route. Host routes in IPv6 are /128, /32. Multicast Multicast is a bit different in IPv6, though the basic principle is the same. The first thing you should notice is that there is no concept of a broadcast in IPv6. If you want to send a packet to all nodes, you sh