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IPv6
Neil Tang
11/10/2008
CS440 Computer Networks
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Outline
 Motivation
 New Features
 IPv6 Addresses
 Autoconfiguration
 Enhanced Routing Functionalities
 Transition from IPv4 to IPv6
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Motivation
 The address space of IPv4 is very limited and will be
exhausted very soon.
 A new Internet Protocol which can provide a much larger
address space is needed.
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New Features
 Address Space: Address field is 128-bit long, i.e., about 3.41038
addresses can be supported.
 Auto-configuration: Hosts can automatically configure themselves such
as their IP addresses.
 Enhanced Routing Functionalities: Routes can be selected on a packetby-packet basis.
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Address Space Allocation
 There is no address class in IPv6. The leading bits specify different
uses of IPv6 addresses. Refer to Table 4.11 in pp.320 for details.
 Unicast Address: This kind of addresses start with “001” and are used
for unicast communications.
 Multicast Address: The addresses starting with “1111 1111” are used for
multicast communications.
 IPv4 Compatible Address: An IPv4 address can be extended to an IPv6
reserved address by prefixing it with 2 bytes of “1” and then zeroextending it.
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Address Notation
 The standard representation is x:x:x:x:x:x:x:x. Each “x” is a hexadecimal
representation of a 16-bit piece of the address. E.g.,
47CD:1234:4422:AC02:0022:1234:A456:0124
 A large number of contiguous 0s can be written more compactly by
omitting all the 0 fields. E.g.,
47CD:0000:0000:0000:0000:0000:A456:0124 -> 47CD::A456:0124
 A reserved IPv6 address containing an embedded IPv4 address can be
represented in a special way. E.g., 128.9.33.81 -> ::FFFF:128.9.33.81.
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Unicast Address
 IPv6 uses a classless addressing scheme. Basically, the CIDR is used
to reduce routing overhead and routing table sizes.
 A stub and a multi-homed AS is usually considered as a subscriber. A
transit AS is usually considered as a provider. There are direct
providers (e.g., regional networks) and indirect providers (e.g.,
backbone networks)
 Based on CIDR, a common prefix is assigned to a provider and then
the provider assigns longer prefixes to its subscribers.
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Unicast Address
The lengths of a particular ID field is not fixed and may be different under
different situations, e.g., a provider with few subscribers might have a
longer ProviderID field than one with many subscribers.
3
m
n
o
p
125- m- n- o- p
010
RegistryID
ProviderID
SubscriberID
SubnetID
InterfaceID
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IPv6 Packet Format
 Version: 6 for IPv6
0
Version
 PayloadLen: the length of the
packet in terms of byte,
excluding the header
 NextHeader: the upper layer
protocol (e.g., TCP or UDP) or
the next extended header.
 HopLimit: same as TTL
4
12
TrafficClass
PayloadLen
16
24
31
Flow Label
NextHeader
HopLimit
SourceAddress
DestinationAddress
Next header/data
 SourceAddress and
DestinationAddress
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Autoconfiguration
 After a host is attached to a network, it first obtains the network prefix
by listening to the periodical advertisement
 Then it combines the prefix with its own physical address (e.g., a 48-bit
Ethernet address) to form a valid IPv6 address.
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Enhanced Routing Functionalities
 In IPv6, the routing header of a packet can contain a list of IPv6
addresses representing a set of routers or backbone networks that the
packet should visit en route to its destination.
 IPv6 defines an anycast address which can be assigned to a set of
routers. A packet including an anycast address will go to the nearest of
those routers.
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Transition from IPv4 to IPv6
 Dual-Stack Operation: Each host or router runs both IPv4 protocol stack
and IPv6 stack.
 Tunneling: The IPv6 packet is encapsulated within an IPv4 header by a
tunnel endpoint and transmitted across the IPv4-only network, and then
is decapsulated by the endpoint on another end.
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