IPv6 solves the address-space limitations of IPv4 and introduces a much larger 128-bit address space. In this lesson you'll learn how IPv6 addresses are written, shortened and categorised, plus the basic ideas behind link-local addressing and neighbour discovery.
IPv6 uses hexadecimal notation instead of dotted decimal. An address is normally written as eight groups of four hexadecimal digits, separated by colons.
Hexadecimal uses the symbols 0–9 and A–F. Each hexadecimal digit represents four binary bits, which makes long binary values much easier to write.
Decimal 10 = A
Decimal 15 = F
Binary 1111 = F
Binary 1010 = A
IPv6 provides two important rules for shortening addresses.
Leading zeros inside each 16-bit group can be removed.
2001:0db8:0000:0001:0000:0000:0000:0001
becomes:
2001:db8:0:1:0:0:0:1
One consecutive run of all-zero groups can be replaced with
::.
2001:db8:0:1:0:0:0:1
becomes:
2001:db8:0:1::1
:: can normally appear only once in a compressed IPv6
address, otherwise the missing number of zero groups would be ambiguous.
2000::/3
Globally routable IPv6 addresses used for communication across IPv6 networks and the Internet.
FE80::/10
Used for communication on the local link. IPv6 interfaces normally have a link-local address even when they also have a global address.
FF00::/8
Used to send traffic to groups of IPv6 devices. IPv6 uses multicast extensively.
::1
IPv6 loopback address, equivalent in purpose to IPv4
127.0.0.1.
::
Represents the absence of an IPv6 address and may be used before a device has configured an address.
FC00::/7
Intended for local or private-style IPv6 communication and not normally routed across the public Internet.
IPv6 devices use link-local addresses for communication with neighbours on the same local link.
They begin within FE80::/10 and are not forwarded by
routers beyond the local link.
Like IPv4, IPv6 uses prefix lengths to indicate how much of an address identifies the network.
A very common IPv6 LAN prefix length is /64.
2001:db8:1234:10::/64
With a /64, the remaining 64 bits identify the interface on that subnet.
xxxx:xxxx:xxxx:xxxx
IPv6 uses Neighbour Discovery Protocol (NDP), which operates using ICMPv6, for functions that include discovering neighbouring devices and resolving Layer 2 addresses.
Needs to reach a neighbour
Neighbour Solicitation
Neighbour Advertisement
IPv6 supports multiple configuration methods.
Static configuration
An administrator manually configures the address and prefix.
SLAAC
Stateless Address Autoconfiguration allows a host to build an address
using information advertised by a router.
DHCPv6
DHCPv6 can provide IPv6 configuration information to clients.
Next we'll move up to Layer 4 and look at TCP versus UDP, port numbers, the TCP handshake, reliability and the common services you'll need to recognise for CCNA.