the necessary evil...

ipv6

larger address space

128 bits binary, 32 hex digits
enhanced reachability and flexibility
prefix aggregation for routing
multihoming
autoconfiguration that includes hardware addresses
plug and play
doesn't need public to private translation
address renumbering and modification made simple

simpler header

routing efficiency and scalability
no broadcasts, no broadcast storms
no checksums
simpler header extension
flow labels;  no need to open transport packet to identify traffic flows

mobility, security

mobile ip and ipsec standards functionality built in
ipsec enabled on every node

incorporation with ipv4

dual stack; ipv6 and ipv4 on the same INTERFACE
tunneling; if you can't stack, tunnel
NAT translation between ipv6 and ipv4 in IOS since 12.3(2)T

32 hex numbers in 8 quartets of 4 hex digits separated by colons
   omit leading zeros
   a single instance of consecutive quartets of zero's can be represented by a double colon (quartet = 1 set of
   4 digits hex times 8 for total

a prefix equals a block of consecutive ipv6 addresses and is represented in routing tables
prefix values need to fall on quartet boundaries or include all values in the last quartet