Key differences between IPv6 and IPv4

IPv6 address is written in hexadecimal format
2001:240:5ff:0:220:e0ff:fe8d:3a8c
Subnet mask is always /64
No variable subnet masks like /28, /29, and stuff
(you will see /n routes in routing table, of course)
It is normal to associate multiple address to an interface
With IPv4, it was normally assumed that a node has single IPv4 address
Scoped IPv6 addresses
Link-local address and site-local address - 128bit is not enough to disambiguate destination
fe80::1%interface1
fe80::1
  |
==+=== ethernet B
  | interface 2
my machine
  | interface 1
==+=== ethernet A
  |
fe80::1