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3. IPv6 Address Architecture
Addresses similar to IPv4
IPv6 addresses identify interfaces (not nodes)
Hierarchical, topological addresses
Forwarding based on best match
Some extra flexibility provided
eg, anycast,auto-configuration
Local node and link addresses available
Easier address change supported
<draft-ietf-ipngwg-addr-arch-v3-07.txt> updates
RFC 2373
4. IPv6 Address Types
Unicast
Identifies a single interface
Packet sent to a unicast address is delivered to the interface identifiedby that
address
Anycast
Identifies a set of interfaces (typicallyon different nodes)
Packet sent to an anycastaddress is delivered to one of the interfaces identified
by that address (normally the nearest)
Multicast
Identifies a set of interfaces (typicallyon different nodes)
Packet sent to a multicast address is delivered to all interfaces identifiedby that
address
IPv6 has no broadcast address
5. IPv6 Address Representation
128 bit length (16 octets)
Represented as 8 * 16-bit pieces in hexadecimal,
separated by colons ":"
For prefixes: IPv6-address/length
(bits)
Multiple 16-bit fields of zeros can be compacted by
using a double-colon "::"
Compaction only used once per address
Low order 32 bits can use v4 format “d.d.d.d“
7. Examples
2001 : 0DB8 : 0000 : 000B : 02AA : 0000 : 0000 : 005A
Rules to follow:
1. Preceding zeros for each 16 bit field can be omitted
2001 : DB8 : 0000 : B : 2AA : 0000 : 0000 : 5A
2. Longest consecutive fields of all zeros can be compressed using ::
2001 : DB8 : 0: B : 2AA : : 5A
3. Consecutive fields of all zeros can be compressed using ::
(But can only be used once)
2001 : DB8 : 0 : B : 2AA : : 5A
8. IPv6 Address Types
High order bits define IPv6 address type
Current IPv6 prefix allocation
Special format addresses (0000::/8)
(unspecified and loopback addresses)
Link-local unicast addresses (FE80::/10)
Site-local unicast addresses (FEC0::/10)
Multicast addresses (FF00::/8)
Aggregatable global unicast addresses (other)
Anycast addresses are allocated from unicast space
13. Aggregatable Global Unicast Address
May be used to connect to public internet
Globally unique
Based on topology Efficient routing
Supports provider-based and exchange-based
aggregation
15. Addressing Hierarchy
ISP 1
ISP 2
ISP 3
ISP 4
IX1 IX2
S1 P1
S2
S3
P2
S4 S5
Public
Site
ISP = Internet Service Provider
IX = Internet Exchange Point
Sn = Site n
Pm = Provider m
S6
16. Address Hierarchy Explained
Currently 3 levels defined
Public
Site
Interface
Both Public and Site topology can be further
subdivided to create even more hierarchies
18. Understanding Interface Identifier
Unique to the link
Identifies interface on a specific link
All except multicast addresses, must have EUI-64 format
MAC-to-EUI-64conversion
1. First three octets of MAC becomes Company-ID
2. Last three octets of MAC becomes Node-ID
3. 0xFFFE is inserted between Company-ID and Node-ID
4. Universal/Local-Bit (U/L-bit) is set to 1 for global scope
19. Understanding Interface Identifier
Interface ID can be generated in many different ways:
Build one from the layer 2 address in the modified EUI-64 format. For the interface ID
portion of the network, the seventh high-order bit of the EUI-64 format defines a local
scope when set to 0 and a global scope (globally unique) when set to 1. Different
mechanisms are defined for each media type to build the complete interface ID in the
modified EUI-64 format.
Autogenerate a random address as defined in RFC 3041. This assignment mechanism was
developed mainly to limit the exposure of a globally reachable address and to increase
privacy.
Acquire the interface ID via DHCPv6.
Manual configuration.
Cryptographically generated addresses (CGAs) based on RFC 3972 through a hash that
includes a public key. This method of generating an interface ID provides added security and
enables address authentication.
20. Autoconfiguration: EUI- 64
MAC Address: 0000:0B0A:2D51
In binary:
00000000 00000000 00001011 00001010 00101101 01010001
◆ Insert FFFE between Company-ID and Node-ID
00000000 00000000 00001011 11111111 11111110 00001010 00101101 01010001
◆ Set U/L bit to 1
00000010 00000000 00001011 11111111 11111110 00001010 00101101 01010001
Resulting EUI-64 Address: 0200:0BFF:FE0A:2D51
22. Special Addresses: Unspecified
Address
Format: 0:0:0:0:0:0:0:0 (all zeros)
MUST NEVER be assigned to any node
Represents absence of an address
MUST NEVER be used as destination address in
IPv6 packets nor in IPv6 routing headers
Used for host initialization (i.e. autoconfiguration)
24. Special Addresses: Loopback Address
Format: 0:0:0:0:0:0:0:1
Analogous to IPv4 loopback 127.0.0.1
Can NEVER be assigned to any physical interface
Used by nodes to send packets to themselves
Traffic destined to loopback address MUST NEVER
leave the sending node
25. Special Addresses: IPv6 with Embedded
IPv4 Address
Format: ::a.a.a.a
Used for dual-stack nodes with v4 and v6
IPv6 address assignment is based on v4 address
Used for automatictunnels
IPv6 automaticallyencapsulated over IPv4
This transition approach is not currently
recommended
(has been replaced by other approaches)
27. Special Addresses: Link-Local Address
Local significance only
Meaningful only to nodes on a single link within a single site
NOT globally unique
Unique only within respective scope
Used for autoconfiguration, neighbor discovery, nodes on
routerless links, routing protocols
Routers MUST NOT forward packets with either source or
destination link-local addresses beyond that link
30. Special Addresses: Link-Local Address
Format
Interface-ID
1111111010 0
10 54 64
128 bit
Examples
FE80:0000:0000:0000:5ABC:01FF:FE01:1111
FE80::0060:08FF:FEB1:7EA2
FE80::200:CFF:FE0A:2C51
31. Special Addresses: Site Local Address
To be used within a site only
NOT globally unique
Recommended for router interfaces
NOT to be propagated beyond site boundaries
Network configured with site-local address is NOT
reachable from locations OUTSIDE the site
Edge routers MUST keep site-local traffic within
site
32. Special Addresses: Site Local Address
Format
Interface-ID
1111111011 0
10 54 64
128 bit
Subnet-ID
(SLA-ID)
16
◆ Examples
FEC0:0000:0000:0000:5ABC:01FF:FE01:1111
FEC0::0060:08FF:FEB1:7EA2
FEC0::200:CFF:FE0A:2C51
33. Special Addresses: Anycast Address
Used to address multiple interfaces on different
nodes with SAME IPv6 address
Allocatedfrom unicast address space
Addresses are taken from Interface-ID field
Currently, only specified anycast addresses are for
subnet-router and for Mobile IPv6 home-agents
34. Special Addresses: Anycast Explained
3 Hops away
4 Hops away
HTTP
HTTP
NTP
NTP
Host
Example:
NTP Servers use the same
anycast addresses.
Anycast takes shortest link to
NTP server.
Host
35. Special Addresses: Subnet Router
Anycast Address
Examples
Subnet-routeranycastaddress: FEC0:0:0:A::
Resulting Unicast routeraddress: FEC0:0:0:A:200:CFF:FE0A:2C51
00000000000000000
Subnet Prefix
n Bits 128-n Bits
128 bit
Subnet
FEC0:0:0:A::
Interface-ID
200:CFF:FE0A:2C51
Interface-ID
200:CFF:FE0C:4A72
36. Special Addresses: Multicast Address
Always begin with 0xFF
Two types
Well-known – assigned by an official authority
Transient – locally assigned for non-global use
Multicast addresses are scoped
Currently 5 scope levels defined:
Local to the node (scope = 1, node-local)
Local to the link (scope = 2, link-local)
Local to the site (scope = 5, site-local)
Local to the organization(scope = 8)
Global (scope = E)
Reserved (scope = 0 and scope = F)
39. Special Addresses: Multicast Address
Format
First 3 bits set to 0
Last bit defines address type:
0000 = Permanent (or well-known)
0001 = Locally assigned (or transient)
42. Special Addresses: Solicited Node
Multicast Address
To identify all nodes for the link-local scope, the following
address is defined:
FF02::1 (link-local scope all-nodes multicast address)
To identify all routers for the link-local scope, the following
address is defined:
FF02::2 (link-local scope all-routers multicast address)
Multicast address can only be a destination address not source
address !!!!
43. Special Addresses: Required IPv6
Address For Hosts
Link-local address for each interface
All assigned unicast addresses
Loopback address
All-nodes multicast addresses
Solicited-node multicast address for each of its assigned
unicast and anycast addresses
Multicast addresses of all other groups to which the host
belongs
A host is required to recognize the following addresses:
45. Special Addresses: Required IPv6
Address For Routers
Subnet-router anycast address for each of its routing
interfaces
All other anycast addresses configured on the router
All-routers multicast address
Multicast addresses of all other groups to which the router
belongs
In addition to the host address requirements a router is
required to recognize the following addresses:
46. Special Addresses: Multihoming
Multi-Homed domains are common
Are a “challenge” for topological addressing
IPv6 requires hosts and DNS to deal with multiple
addresses for a host
<draft-ietf-ipngwg-default-addr-select-06.txt> is a
proposal for how hosts select addresses to use for any
particular communication
This provides one possible solution
An alternative: Exchange-based addresses
More work is needed in this area
47. IPv4 & IPv6 Comparison
IPv4 Address IPv6 Address
Internet address classes Not applicable in IPv6
Multicast address (224.0.0.0/4) IPv6 multicast addresses (FF::/8)
Broadcast address Not applicable in IPv6
Unspecified address is 0.0.0.0 Unspecified address is ::
Loopback address is 127.0.0.1 Loopback address is ::1
Public IP address Global unicast addresses
Private IP addresses Link local addresses (FE80::/64)
(10.0.0.0, 172.16.0.0, 192.168.0.0)
Dotted-decimal notation Colon hexadecimal format
10.2.3.96 2404:1234::236:ABCD
Prefix representation Prefix representation
Subnet mask /48 or /52 or etc
Eg: 255.255.254.0
