IPv4 versus IPv6

Internet communication would not be possible without the Domain Name System (DNS). For humans to interact with computers, there is a need for a translator that can translate human readable addresses into addresses that a computer can understand and act upon. Thus, DNS is used to translate computer readable binary into and from human readable IP addresses. DNS takes the process a step further by having records associating IP addresses to their respective common language addresses. The common denominator in DNS is the Internet Protocol address, also known as the IP address. To put it plainly, an IP address is a house number or a mailbox number and it identifies the location to which, or from which, data is communicated.

Since September of 1981, the standard for identifying network hosts has been IPv4, also known as Request For Comment (RFC) 791 [2]. The RFC document provides specifications for the Internet Protocol per standards defined by the U.S. Department of Defense. IPv4, at the time of its creation, was the fourth revision, or version, of the Internet Protocol. The RFC established all aspects relating to network communication using the Internet Protocol, including addressing and security [2]. IPv4 has been the standard for network communication for more than 30 years, until now. Global IPv4 address availability is on the verge of becoming exhausted [3]. As a result of the growth of the mobile device market and the emergence of the Internet of Things, IPv4 addressing is becoming extinct.

The Internet Engineering Task Force (IETF), responsible for making the Internet work better, approved RFC 2460, which is the Internet Protocol version 6, or IPv6. RFC 2460 was approved in 1998 and introduced the new standard for network addressing. Its introduction and eventual adoption as the standard by which all networked device communicate will allow for 340 undecillion addresses to be available. That equates to 3.4 billion, billion, billion IP addresses, more than enough for every person on the planet to have 4.8x1028 devices. While it is good to know that there is a solution on the horizon to solve the extinction of IPv4 addresses, there are some differences related to the integration of IPv6 into the IPv4 environment, and it all starts with DNS.

IPv4 Standard

The IPv4 standard uses 32-bit addresses in a dot decimal notation that looks like this:

xxx.xxx.xxx.xxx

The “x” is replaced by a number between 0 and 255 in each of the four sections (also called octets). IPv4 addresses are divided into five distinct classes, class A through class E. Each class has a different bit length that comprises the addressing of the network host. The class A IPv4 address uses the first octet, or section, of an IPv4 address for the network identifier, with the remaining octets reserved for host identification. The class C IPv4 address uses the first three octets, or sections, for network identification, with the fourth and final octet reserved for host identification.

IPv6 Standard

The IPv6 standard uses a significantly more complex address that is 128-bits in length, as opposed to IPv4’s 32-bit length. While the IPv4 address is explicitly decimal, the IPv6 address uses hexadecimal to represent an IP address. The format for an IPv6 address is 32 hexadecimal characters separated by a colon into eight groups of four characters.

An example of what an IPv6 address looks like is as follows:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

The IPv6 standard allows for a shortcut to reduce the length of the address visually by removing subsequent groups of zeroes and replacing them with a double colon. Using the example address above, it could be written like this:

2001:0db8:85a3::8a2e:0370:7334

This is known as zero compression, where repeated groupings of zeroes are trimmed down and any leading zeroes are removed [1].

DNS with IPv4 and IPv6

In DNS, the IPv4 address is configured as a host record, also known as an A record, and is used to resolve a host name, for example, domain.com, to the IP address of the server that supports that domain.

DNS is also used to configure a reverse lookup for an IPv4 address so that a computer can locate the host of a particular IP address. By writing the IPv4 address backwards and adding “.in-addr.arpa” afterwards, a reverse lookup zone can be created.

An example of an IPv4 address is:

8.8.4.4

This is an IPv4 address that Google owns and is configured as a DNS A record. The reverse lookup for this DNS zone record would look like this:

4.4.8.8.in-addr.arpa

The IPv6 record in DNS is known as an AAAA record, read aloud as “Quad-A”, and is used to map a host name to the IPv6 address [1]. The new IPv6 standard also introduces a new reverse lookup record for DNS, but its format is similar to that of the IPv4 standard. The IPv6 address is written backwards, just like in IPv4, but it is then followed by “ip6.arpa”.

Using the address provided in the above IPv6 example, the zero compression must be removed first, and then the IPv6 address can be written in reverse:

4.3.3.7.0.7.3.0.e.2.a.8.0.0.0.0.0.0.0.0.3.a.5.8.8.b.d.0.1.0.0.2.ip6.arpa

The reverse lookup zone in DNS is created automatically for IPv4 and IPv6 addresses when the initial forward lookup zone is created.

Summary

Although IPv6 looks complicated on the surface, it is meant to behave in much the same way as the traditional IPv4 standard. There are benefits to utilizing the IPv6 standard over IPv4, one of which has already been mentioned, and that is the additional IP addresses that will be available. Additional benefits include more efficient routing and packet processing, simplified network configuration, and security [4].

In terms of using IPv6 with DNS, the result is a smaller DNS table and more efficient assignment and interaction with network nodes. For systems and network administrators, the auto-configuration of IPv6 addresses is an improvement over IPv4, particularly because of IPv6’s use of a device’s MAC address as part of the IPv6 address.

While IPv4 and IPv6 share features and rules, it is the scale of support that makes IPv6 the new go-to standard for IP addressing. The enormous amount of available addresses in IPv6 along with additional benefits like anycast, auto-configuration, and simplified IP assignment, ensure the future of the new standard. Internet Service Providers are upgrading their equipment to support IPv6, as are device and computer manufacturers all over the world. In the next few years, IPv6 will be the new IP addressing scheme for the Internet.

References

[1] Horley, E. (2013). Practical ipv6 for windows administrators. Retrieved from http://common.books24x7.com.lib.kaplan.edu/toc.aspx?bookid=62121

[2] Internet protocol. (September, 1981). Retrieved from https://tools.ietf.org/html/rfc791

[3] Li, Q., Qin, T., Guan, X., & Zheng, Q. (April 29, 2014). Exploring flow characteristics in ipv6: A comparative measurement study with ipv4 for traffic monitoring. KSII Transactions On Internet & Information Systems, 8(4), 1307-1323. doi:10.3837/tiis.2014.04.009

[4] Park, S., Jeong, J., & Hong, C. (July 18, 2012). DNS configuration in ipv6: Approaches, analysis, and deployment scenarios. IEEE Computer Society, 17(4), 48-56. doi:10.1109/MIC.2012.96