Chapter 3 IPv6 Addressing 53 are permitted in RFC 4291,in practice their prefix lengths are always 64 and therefore do not need to be expressed.For example,there is no need to express the IPv6 unicast address 2001:DB8::2AC4:2AA:FF:FE9A:82D4 as 2001:DB8::2AC4:2AA:FF:FE9A:82D4/64.Because of the 50-50 split of subnet prefixes and interface identifiers,the unicast IPv6 address 2001:DB8::2AC4:2AA:FF:FE9A:82D4 implies that the subnet prefix is 2001:DB8:0:0:2AC4:/64. Note Address prefixes with a prefix length longer than 64 bits can be used for point-to- point links between routers. Types of IPv6 Addresses There are three types of IPv6 addresses: Unicast A unicast address identifies a single interface within the scope of the type of address.The scope of an address is the region of the IPv6 network over which the address is unique.With the appropriate unicast routing topology,packets addressed to a unicast address are delivered to a single interface.To accommodate load-balancing systems,RFC 4291 allows for multiple interfaces to use the same address as long as they appear as a single interface to the IPv6 implementation on the host. Multicast A multicast address identifies zero or more interfaces on the same or different hosts.With the appropriate multicast routing topology,packets addressed to a multicast address are delivered to all interfaces identified by the address. Anycast An anycast address identifies multiple interfaces.With the appropriate unicast routing topol- ogy,packets addressed to an anycast address are delivered to a single interface-the nearest interface that is identified by the address.The nearest interface is defined as being the closest in terms of routing distance.A multicast address is used for one-to-many communication, with delivery to multiple interfaces.An anycast address is used for one-to-one-of-many communication,with delivery to a single interface. In all cases,IPv6 addresses identify interfaces,not nodes.A node is identified by any unicast address assigned to any one of its interfaces. Note RFC 4291 does not define a broadcast address.All types of IPv4 broadcast addressing are performed in IPv6 using multicast addresses.For example,the subnet and limited broadcast addresses from IPv4 are replaced with the link-local scope all-nodes multicast address of FF02::1.￾     !"#$%&''()*+,(-+./-0"()111 12*--3 1*+&(-11*--(45607'--- #88%9:;<99#=!"9#==9 9 >$=9<#:"-#88%9:;<99#=!"9#==9 9 >$=9<#:"?0"3;'7-1) (@8A@8-+1)-72)*-)')-&(7'-4560-- #88%9:;<99#=!"9#==9 9 >$=9<#:"+-((-72)*-#88%9:;<98989#=!"99?0"3 BC DEEFGHHIFGJKLGHMKNOPIFGJKLQGRSNOQTRSGFNOPRUVWKNHXPRWGYHGEJTFITKRNZNTZ ITKRNQKR[HWGNMGGRFTYNGFH\ ]^_`abcdefghiij`aa`a k((/-1)4560---9 lmnopqr =7'---)--,+)'.((-'11)(/1)--3k( -'11)---(,11)(4560.1s16.('((---7t73u( (17'-17,11+1,/&'s---17'---+6 1-,+)'3k1''11+1A2+',-/--& !"#$%++1.-)17++ )'-17-(----+1,-(/--,+)'1(4560 +11((1-3 vwxrnopqr =7+'---)-y111)'-1(-1))(1--3u(( 17+'-17,11+1,/&'s---17+'---+6 1++)'-)2/(--3 zm{opqr =/'---)-7++)'-3u((17'-17,11+A 1,/&'s---1/'---+61-,+)'|(- )'(-)2/(--3k(-)'-)-2,('+1-- -1)17,-'3=7+'----7-)11A1A/'17'1& .(+6/17++)'-3=/'----7-)11A1A1A1)A/ '17'1&.(+6/1-,+)'3 4++'--&4560---)/)'-&11-3=1-)2//7'- ----,1/11)-)'-3 BC }~V€‚ETGHRTNEGJKRGPWFTPEXPHNPEEFGHH\DQQNƒIGHTJ„…†VWFTPEXPHNPEEFGHHKRS PFGIGFJTF‡GEKR„…†UYHKRS‡YQNKXPHNPEEFGHHGH\~TFGLP‡IQGˆNOGHYWRGNPREQK‡KNGE WFTPEXPHNPEEFGHHGHJFT‡„…†VPFGFGIQPXGEMKNONOGQKR[ZQTXPQHXTIGPQQZRTEGH‡YQNKXPHN PEEFGHHTJ~~‰€ŠŠ‚\