Operating Systems

IBM System z: IPv6 Status

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The Internet Protocol, IPv6, will become more important in the coming years as the IPv4-based Internet reaches its address limitation. This article explains the shortcomings of the IPv4 standard and how IPv6 solves these. The operating systems used on IBM System z are checked to verify readiness for the new standard. Results of the verification tests published by the IPv6 Forum are listed and describe how we apply these test suites to the latest Linux distributions used on System z.

Brief Review of IPv4

The Internet Protocol (IP) is the component responsible for packet delivery in packet-switched networks. The formal specification of IPv4 emerged in 1980 with the introduction of 4-byte addresses for network nodes. From the beginning of the worldwide Internet, IPv4 was an integral part.

To simplify address allocation, an IP address was divided into two parts—the network identifier and host identifier. The network identifier was comprised of 1, 2, or 3 bytes (Class A, B, or C) and the rest of the address was used to identify a host in that network. By the ‘90s, the success of the Internet and the address allocation based on the network classes revealed that the size of the IP address was a limiting factor.

To lower the consumption rate of IP addresses, two concepts where proposed: To lower the demand for public IP addresses, it became possible to access the Internet from private networks via Network Address Translation (NAT). To allow for more efficient address allocation, Classless Inter-Domain Routing (CIDR) was introduced.

Both concepts were considered interim solutions; they wouldn’t solve the IPv4 address exhaustion problem. Serious forecasts mentioned February 2011 as the date when the Internet Assigned Numbers Authority (IANA) allocates the last chunk of IP addresses to the downstream Regional Internet Registries (RIRs). However, it’s expected that the RIRs can supply IP addresses to Internet Service Providers (ISPs) and local Internet registries for an additional six months (see www.potaroo.net/tools/index.html for the most current dates). For an official statement on IPv4 address depletion, check the American Registry for Internet Numbers (ARIN) at https://www.arin.net/. Because the assigned IPv4 addresses don’t allow building efficient hierarchies that can be aggregated (i.e., the routing table basically contains one entry for each network), the IPv4 routing process is a tedious, slow task.

In 1993, the Internet Engineering Task Force (IETF) released a white paper solicitation for requirements and selection criteria of the next generation of IP (IPng), later termed IPv6. The first formal specification of IPv6 was presented in December 1995.

Basics of IPv6

The foremost goal of the IPv6 specification is to have a much larger address space than IPv4. The initial specification was revised in 1998 and Request For Comments (RFC) 2460 continues to serve today as the architectural blueprint. With the 16-byte (128-bit) addresses of IPv6, no limitation of the address space of the network layer is conceivable.

Addresses and names: The IPv6 addressing architecture was revised several times; the latest specification is RFC 4291 from 2006. It defines three types of addresses:

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