50 Understanding IPv6,Second Edition It is easy to get lost in the vastness of the IPv6 address space.As we will discover,the unthink- ably large 128-bit IPv6 address that is assigned to an interface on a typical IPv6 host is com- posed of a 64-bit subnet prefix and a 64-bit interface identifier(a 50-50 split between subnet space and interface space).The 64 bits of subnet prefix leave enough addressing room to satisfy the addressing requirements of the levels of Internet service providers(ISPs)between your organization and the backbone of the Internet and the addressing needs of your organi- zation.The 64 bits of interface identifier accommodate the mapping of current and future link-layer media access control (MAC)addresses. IPv6 Address Syntax IPv4 addresses are represented in dotted-decimal format.The 32-bit IPy4 address is divided along 8-bit boundaries.Each set of 8 bits is converted to its decimal equivalent and separated by periods.For IPv6,the 128-bit address is divided along 16-bit boundaries,and each 16-bit block is converted to a 4-digit hexadecimal number and separated by colons.The resulting representation is called colon hexadecimal. The following is an IPv6 address in binary form: 0010000000000001000011011011100000000000000000000010111100111011 0000001010101010000000001111111111111110001010001001110001011010 The 128-bit address is divided along 16-bit boundaries: 0010000000000001000011011011100000000000000000000010111100111011 0000001010101010 0000000011111111 1111111000101000 1001110001011010 Each 16-bit block is converted to hexadecimal and delimited with colons.The result is the fol- lowing: 2001:0DB8:0000:2F3B:02AA:00FF:FE28:9C5A IPv6 address representation is further simplified by suppressing the leading zeros within each 16-bit block.However,each block must have at least a single digit.With leading zero suppres- sion,the result is the following: 2001:DB8:0:2F3B:2AA:FfF:FE28:9C5A Number System Choice for IPv6 IPv6 uses hexadecimal(the Base 6 numbering system),rather than decimal(the Base1o numbering system),because it is easier to convert between hexadecimal and binary than it is to convert between decimal and binary.Each hexadecimal digit represents four binary digits.￾  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` aabaaaaaaaaaaaabaaaabbabbabbbaaaaaaaaaaaaaaaaaaaaababbbbaabbbabb aaaaaabababababaaaaaaaaabbbbbbbbbbbbbbbaaababaaabaabbbaaababbaba =" 34512 ''(  '#''  ! 3&12 2/!'(` aabaaaaaaaaaaaab aaaabbabbabbbaaa aaaaaaaaaaaaaaaa aababbbbaabbbabb aaaaaabababababa aaaaaaaabbbbbbbb bbbbbbbaaababaaa baabbbaaababbaba S*" 3&12 2 *0  *!#('  "8'*6 !' ' 6' -" * !+ =" (/   " $ 1 -!` caabdaefgdaaaadchifdacjjdaahhdhkcgdlmnj %#& ''( ()(!!  $/("( 6) $' 2 /))(! " '! @( -"! *" 3&12 2 *0+ o-#(. *" 2 *0 6/ "#    !  '+ p" '! @( /))(1 !. " (/   " $ -!` caabdefgdadchifdcjjdhhdhkcgdlmnj qrstJI LMKOJs uvwxyJ zwI CDEF %#& / "8'*6 9" {3& !/62(! 6<. ("( "! '*6 9" {3; !/62(! 6<. 2*/   (  *!#( 2-! "8'*6 !' 2!( "!    *!#( 2-! '*6 !' 2!(+ S*" "8'*6 ' ()(! $/( 2!( '+