1 IPv6: Address Architecture Dr. Rocky K. C. Chang 29 January, 2002

2 Address architecture IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces. There are three types of addresses: –Unicast: An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. –Anycast and multicast: An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces identified by that address (the "nearest" one, according to the routing protocols' measure of distance). A packet sent to a multicast address is delivered to all interfaces identified by that address.

3 Address architecture There are no broadcast addresses in IPv6, their function being superseded by multicast addresses. All interfaces are required to have at least one link- local unicast address. A single interface may also be assigned multiple IPv6 addresses of any type (unicast, anycast, and multicast) or scope.

4 Notation of IPv6 addresses The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hexadecimal values of the eight 16-bit pieces of the address. Examples: –FEDC:BA98:7654:3210:FEDC:BA98:7654:3210 –1080:0:0:0:8:800:200C:417A Compressing a string of 0s –The use of "::" indicates multiple groups of 16-bits of zeros. –The "::" can only appear once in an address. – The "::" can also be used to compress the leading and/or trailing zeros in an address.

5 Notation of IPv6 addresses –For example, the following addresses 1080:0:0:0:8:800:200C:417A a unicast address FF01:0:0:0:0:0:0:101 a multicast address 0:0:0:0:0:0:0:1 the loopback address 0:0:0:0:0:0:0:0 the unspecified addresses –may be represented as: 1080::8:800:200C:417A a unicast address FF01::101 a multicast address ::1 the loopback address :: the unspecified addresses

6 Notation of IPv6 addresses An alternative for a mixed environment of IPv4 and IPv6 nodes is x:x:x:x:x:x:d.d.d.d, –where the 'x's are the hexadecimal values of the six high- order 16-bit pieces of the address, and –the 'd's are the decimal values of the four low-order 8-bit pieces of the address (standard IPv4 representation). –Examples: 0:0:0:0:0:0: and 0:0:0:0:0:FFFF: or in compressed form: :: and ::FFFF: Address prefixes: ipv6-address/prefix-length, e.g., –12AB:0000:0000:CD30:0000:0000:0000:0000/60 –12AB::CD30:0:0:0:0/60 –12AB:0:0:CD30::/60

7 Required addresses A host is required to recognize the following addresses as identifying itself: –Its link-local address for each interface –Assigned unicast addresses –Loopback address (::1) –A number of multicast addresses, including All-Nodes multicast address (FF01:0:0:0:0:0:0:1 and FF02:0:0:0:0:0:0:1) In addition to above, a router is required to recognize –Subnet-Router anycast address and –All-Routers multicast addresses (FF05:0:0:0:0:0:0:2).

8 Address type representation

9 Fifteen percent of the address space is initially allocated. The remaining 85% is reserved for future use. Unicast addresses are distinguished from multicast addresses by the value of the high-order octet of the addresses. –A value of FF ( ) identifies an address as a multicast address; –Any other value identifies an address as a unicast address. Anycast addresses are taken from the unicast address space, and are not syntactically distinguishable from unicast addresses.

10 Aggregatable global unicast addresses IPv6 unicast addresses are designed assuming that the Internet routing system –makes forwarding decisions based on a "longest prefix match" algorithm on arbitrary bit boundaries and –does not have any knowledge of the internal structure of IPv6 addresses. The structure in IPv6 addresses is for assignment and allocation. The only exception to this is the distinction made between unicast and multicast addresses.

11 This address format is designed to support both the current provider-based aggregation and a new type of exchange-based aggregation. Aggregatable addresses are organized into a three level hierarchy: –Public Topology: a collection of providers and exchanges who provide public Internet transit services. –Site Topology: local to a specific site or organization which does not provide public transit service to nodes outside of the site. –Interface Identifier: identify interfaces on links. Aggregatable global unicast addresses

12 An example

13 Aggregatable global unicast addresses Terms: –P1, P2, P3: long-haul providers; X1, X2: exchanges –P5, P6: multiple levels of providers; S.x: subscribers Exchanges will allocate IPv6 addresses. –Organizations who connect to these exchanges will also subscribe (directly, indirectly via the exchange, etc.) for long-haul service from one or more long-haul providers. –Doing so, they will be able to change long-haul providers without having to renumber. –They can also be multihomed via the exchange to more than one long-haul provider without having to have address prefixes from each long-haul provider.

14 Aggregatable global unicast addr. structure

15 Top and next level aggregation Top-Level Aggregation Identifier –Default-free routers must have a routing table entry for every active TLA ID (8192 of them). –Additional TLA IDs may be added by either growing the TLA field to the right into the reserved field or by using this format for additional format prefixes. Next-Level Aggregation Identifier –These identifiers are used by organizations assigned a TLA ID to create an addressing hierarchy and to identify sites. –The organization can assign the top part of the NLA ID in a manner to create an addressing hierarchy appropriate to its network.

16 Top and next level aggregation –Organizations assigned TLA IDs may also support NLA IDs in their own Site ID space. This allows the organization assigned a TLA ID to provide service to organizations providing public transit service and to organizations who do not provide public transit service.

17 Next level aggregation

18 Site level aggregation Site-Level Aggregation Identifier –The SLA ID field is used by an individual organization to create its own local addressing hierarchy and to identify subnets. –A site may create a two or more level hierarchy in the SLA ID field:

19 Interface identifier Interface Identifier –These identifiers are used to identify interfaces on a link. They are required to be unique on that link. –In many cases an interface identifier will be the same or be based on the interface's link-layer address. –Interface IDs used in the aggregatable global unicast address format are required to be 64 bits long and to be constructed in IEEE EUI-64. These identifiers may have global scope when a global token (e.g., IEEE 48bit MAC) is available or may have local scope where a global token is not available (e.g., serial links, tunnel end-points, etc.). –Stateless (RFC 2462) and stateful configuration (DHCP)

20 Special addresses Unspecified addresses (0:0:0:0:0:0:0:0 ) –It must never be assigned to any node. It indicates the absence of an address. –One example of its use is in the Source Address field of any IPv6 packets sent by an initializing host before it has learned its own address. –The unspecified address must not be used as the destination address. Loopback addresses (0:0:0:0:0:0:0:1) –An IPv6 packet with a destination address of loopback must never be sent outside of a single node and must never be forwarded by an IPv6 router.

21 Special addresses IPv6 Addresses with Embedded IPv4 Addresses –IPv4-compatible IPv6 address (for IPv6 nodes) –IPv4-mapped IPv6 address (for IPv4 nodes)

22 Special addresses Local-Use IPv6 Unicast Addresses –The Link-Local is for use on a single link. –The Site-Local is for use in a single site.

23 Special addresses –Link-Local addresses are designed to be used for addressing on a single link for purposes such as auto-address configuration, neighbor discovery, or when no routers are present. –Site-Local addresses are designed to be used for addressing inside of a site without the need for a global prefix. –Routers must not forward any packets with site-local or link-local source or destination addresses outside of the site.

24 Anycast addresses When a unicast address is assigned to more than one interface, thus turning it into an anycast address, –the nodes to which the address is assigned must be explicitly configured to know that it is an anycast address. Each member of the anycast set must be advertised as a host route. One expected use of anycast addresses is to identify the set of routers belonging to an organization providing internet service. –Such addresses could be used as intermediate addresses in an IPv6 Routing header, to cause a packet to be delivered via a particular aggregation or sequence of aggregations.

25 Anycast addresses Some other possible uses are to identify the set of routers attached to a particular subnet, or the set of routers providing entry into a particular routing domain. Restrictions: –An anycast address must not be used as the source address of an IPv6 packet. –An anycast address must not be assigned to an IPv6 host, that is, it may be assigned to an IPv6 router only.

26 Address resolution ARP is no longer used by IPv6. Instead, new neighbor discovery protocols are used for address resolution and other functions, such as router solicitation and advertisement. If the address information is not in a host’ (or router’s) cache, it multicasts an ICMP Neighbor Solicitation message. –The target address parameter is set to the address of the solicited neighbor. –The hop count is always set to 1.

27 Acknowledgements The notes are based on –Christian Huitema, IPv6: The New Internet Protocol, Second Edition, 1998, Prentice Hall PTR. –S. Deering and R. Hinden, “Internet Protocol, Version 6 (IPv6) Specification,” RFC 2460, Dec –T. Narten, E. Nordmark, and W. Simpson, “Neighbor Discovery for IP Version 6,” RFC 2461, Dec –R. Hinden and S. Deering, “IP Version 6 Addressing Architecture,” RFC 2373, July –R. Hinden, M. O'Dell, and S. Deering, “An IPv6 Aggregatable Global Unicast Address Format,” RFC 2374, July 1998.