|Managing Serviceguard Fifteenth Edition > Appendix H IPv6
Several IPv6 types of addressing schemes are specified in the RFC 2373 (IPv6 Addressing Architecture). IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces. There are various address formats for IPv6 defined by the RFC 2373. IPv6 addresses are broadly classified as follows:
The following table explains the three types of IPv6 address types: unicast, anycast, and multicast.
Table H-1 IPv6 Address Types
Unlike IPv4, there are no broadcast addresses in IPv6 because their functions are superseded by multicast.
There are three conventional forms for representing IPv6 addresses as text strings:
IPv6 Address Prefix is similar to CIDR in IPv4 and is written in CIDR notation. An IPv6 address prefix is represented by the notation:
IPv6-address/prefix-length where ipv6-address is an IPv6 address in any notation listed above and prefix-length is a decimal value representing how many of the leftmost contiguous bits of the address comprise the prefix. Example:
The first 64-bits of the address fec0:0:0:1 forms the address prefix. An address prefix is used in IPv6 addresses to denote how many bits in the IPv6 address represent the subnet.
IPv6 unicast addresses are classified into different types. They are global aggregatable unicast address, site-local address and link-local address. Typically a unicast address is logically divided as follows:
Interface identifiers in a IPv6 unicast address are used to identify the interfaces on a link. Interface identifiers are required to be unique on that link. The link is generally identified by the subnet prefix.
A unicast address is called an unspecified address if all the bits in the address are zero. Textually it is represented as “::”.
The unicast address ::1 or 0:0:0:0:0:0:0:1 is called the loopback address. It is used by a node to send packets to itself.
There are a number of techniques for using IPv4 addresses within the framework of IPv6 addressing.
The IPv6 transition mechanisms use a technique for tunneling IPv6 packets over the existing IPv4 infrastructure. IPv6 nodes that support such mechanisms use a special kind of IPv6 addresses that carry IPv4 addresses in their lower order 32-bits. These addresses are called IPv4 Compatible IPv6 addresses. They are represented as follows:
Table H-3 Title not available (IPv4 Compatible IPv6 Addresses)
There is a special type of IPv6 address that holds an embedded IPv4 address. This address is used to represent the addresses of IPv4-only nodes as IPv6 addresses. These addresses are used especially by applications that support both IPv6 and IPv4. These addresses are called as IPv4 Mapped IPv6 Addresses. The format of these address is as follows:
The global unicast addresses are globally unique IPv6 addresses. This address format is very well defined in the RFC 2374 (An IPv6 Aggregatable Global Unicast Address Format). The format is:
Table H-5 Title not available (Aggregatable Global Unicast Addresses)
whereFP = Format prefix. Value of this is “001” for Aggregatable Global unicast addresses.TLA ID = Top-level Aggregation Identifier.RES = Reserved for future use.NLA ID = Next-Level Aggregation Identifier.SLA ID = Site-Level Aggregation Identifier.
Interface ID = Interface Identifier.
Link-local addresses have the following format:
Link-local address are supposed to be used for addressing nodes on a single link. Packets originating from or destined to a link-local address will not be forwarded by a router.
Site-local addresses have the following format:
Table H-7 Title not available (Site-Local Addresses)
Link-local address are supposed to be used within a site. Routers will not forward any packet with site-local source or destination address outside the site.
A multicast address is an identifier for a group of nodes. Multicast addresses have the following format:
Table H-8 Title not available (Multicast Addresses)
“FF” at the beginning of the address identifies the address as a multicast address.
The “flgs” field is a set of 4 flags “000T”. The higher order 3 bits are reserved and must be zero. The last bit ‘T’ indicates whether it is permanently assigned or not. A value of zero indicates that it is permanently assigned otherwise it is a temporary assignment.
The “scop” field is a 4-bit field which is used to limit the scope of the multicast group. For example, a value of ‘1’ indicates that it is a node-local multicast group. A value of ‘2’ indicates that the scope is link-local. A value of “5” indicates that the scope is site-local.
The “group ID” field identifies the multicast group. Some frequently used multicast groups are the following:All Node Addresses = FF02:0:0:0:0:0:0:1 (link-local)
All Router Addresses = FF02:0:0:0:0:0:0:2 (link-local)All Router Addresses = FF05:0:0:0:0:0:0:2 (site-local)