The Basics of DNS
DNS is the acronym used for Domain Name System. A primary purpose of DNS is to translate IP addresses into hostnames (alphabetic names) inside a local network and vice versa (Kralicek, 2016). DNS is an essential component of the Internet because this IP conversion creates a much more user-friendly experience. Without DNS, the user would be required to navigate the Internet using numeric (IPv4) or hexadecimal IP (IPv6) addresses. It is much easier for users to remember hostnames that usually consist of easily remembered words. An example of a hostname is Amazon.com. One of the IPv4 addresses that are associated with Amazon.com is 184.108.40.206. For humans, the hostname of Amazon.com is easier to remember than the IPv4 address. There is often the need to remember dozens of web addresses, so DNS is essential. DNS has evolved to become a worldwide network of databases that resolves IP addresses to support internet traffic. DNS works with both IPv4 and IPv6.
The invention of IPv4 came in the 1970s. IPv4 addresses consist of 32-bit numeric characters providing the capability of about 4.3 billion different combinations of numbers. The 32-bit numbers contain four digits separated by periods, as shown in the Amazon.com example above. Each of the four numbers can have a value that ranges from 0 to 255. IPv4 is considered a classful network architecture. There are five classes, but only three are commonly used by hosts on networks. Large organizations such as governments, large universities, large businesses, and large Internet Service Providers use Class A network addresses. Mid-sized companies and organizations use Class B network addresses. Small organizations, businesses, and home offices use Class C network addresses (Panek, 2020).
The development of IPv6 came in the 1990s. The need for IPv6 was driven by the expectation that the approximately 4.3 billion address capacity of IPv4 would be exhausted because of the ever-increasing number of devices that require addresses. IPv6, which
replaces IPv4, solved the address exhaustion problem by using 128-bit address space instead of the 32-bit address space of IPv4. This larger address space gives IPv4 the capability of providing exponentially more addresses than IPv4 (3.4 undecillion addresses) (Kralicek, 2016). IPv6 addresses are divided into eight groups that each contain four hexadecimal digits. Every hexadecimal digit can represent four bits. The preferred form is x:x:x:x:x:x:x:x. Each x is a 16-bit section that can be represented using up to four hexadecimal digits, with the sections separated by colons (Cisco Press, 2017).
Some Advantages of IPv6 over IPv4
Beyond the increase in available address space, IPv6 has some additional advantages over IPv4. In the 1970s, when IPv4 was created, there was less focus on security compared to today. IPv4 required the introduction of security, while IPv6 was designed to have native security baked in. IPv6 utilizes IPSec to provide end-to-end packet encryption that ensures data is transmitted across the network securely.
Another advantage of IPv6 is that it eliminates the need for Network Address Translation (NAT). NAT for IPv4 is a method to deal with the limited number of available IP addresses. NAT works on routers that sit between two networks. It translates private addresses used on a local network to globally unique addresses that can be forwarded to other networks. Using NAT, only a single address gets advertised by the router that connects the network to the outside world. When incoming packets are received, NAT translates again to ensure that the packet is delivered to the correct device within the network. Since IPv6 eliminates the problem of limited address space, IPv6 removes the need for NAT. The removal of NAT from a network is an advantage because it removes a point of failure. Also, the removal of NAT means that less processing is needed resulting in more efficiency and potentially higher data transmission speeds.
IPv6 has configuration advantages over IPv4. In IPv4, network administrators manually assign IP addresses or use Dynamic Host Configuration Protocol (DHCP). DHCP enables temporary IP addresses to be assigned automatically from a pool. The IP addresses are returned to the pool for reassignment after the “IP Lease” expires. IPv6 allows IP addresses to be automatically assigned using Stateless IP Address Autoconfiguration (SLAAC) (Hagen, 2014). With SLAAC, when a new device is added to a network, it can automatically obtain its own IP address without the need for DHCP.
IPv4 supports broadcast transmissions, while IPv6 supports multicast. Broadcast is the sending of data packet(s) to all users on a network without the need to individually address the packet(s) and without the need for a response from the users. In IPv4, a broadcast is sent using a broadcast address. Conversely, IPv6 was designed with the capability of multicast. Multicast sends data to a set of hosts that are predetermined by adding the host addresses to multicast groups (Juniper, 2021). Multicast is more efficient than broadcast because multicast allows the senders to select who receives the transmission. This results in more efficiency within the network since the nodes within the network do not need to continuously listen for and receive broadcast traffic that might not be necessary.
Quality of Service (QoS) is another differentiator between IPv4 and IPv6. QoS is used to control traffic so that performance is guaranteed for specific applications. QoS is applied for bandwidth-intensive applications like Voice Over Internet Protocol (VOIP). VOIP is a protocol that allows phones to work over the network, replacing the need for traditional Plain Old Telephone Service (POTS) phones. If data transmission performance is low (i.e. latency or jitter) for VOIP, the voice quality can be affected. With IPv4, QoS data is included in the packet, and routers are configured to prioritize critical traffic (like VOIP traffic). IPv6 has built-in QoS.
Diferences between IPv4 DNS and IPv6 DNS
The shift from IPv4 to IPv6 does not change the user experience when it comes to DNS. With IPv6, the user will still enter the same hostnames, and the IP address will be resolved in the background, just like when using IPv4. The configuring of IPv6 DNS is also very similar to the process for configuring IPv4 DNS.
There are two types of lookup zones utilized in DNS: Forward Zone and Reverse Zone. Forward lookup zones translate the hostname to the IP address, while reverse lookup zones translate the IP address to the hostname. In IPv4, forward lookup zones are represented using ‘A Records’. ‘A Records’ are only designed to hold 32-bit IP addresses. Since IPv6 addresses are 128 bits, DNS needed a solution that would accommodate the larger IP addresses. The answer came with introducing the ‘AAAA’ (Quad A) record (Liu, 2011). Berkely Internet Name Domain (BIND) is open-source software that is commonly used for DNS servers. BIND currently supports IPv6 and ‘AAAA’ Records. Reverse zone lookups translate hostnames to the IP address. IPv6 uses the IP6.ARPA domain to accomplish reverse zone lookups (Pete, 2004). ARPA is the acronym for Address and Routing Parameters Area. Similarly, IPv4 uses the IP4.ARPA domain for this reverse lookup function.
Advantages of IPv6 DNS
The primary advantage of IPv6 DNS is that it enables the benefits that IPv6 has over IPv4. These include the ample address space, the elimination of NAT, configuration advantages, multicast enablement, QoS, etc.
Another advantage of IPv6 DNS is that it is more secure than IPv4 DNS.
Disadvantages of IPv6 DNS
A disadvantage of IPv6 DNS is that it is not backward compatible with IPv4. Since the IPv6 rollout is a slow process, lasting many years, there is the need for DNS servers to respond to both IPv6 and IPv4 requests. This requirement results in less efficiency until the completion of the IPv6 conversion.
IPv6 may reduce the practice of subnetting. Subnetting is often used in IPv4 to segment networks to increase the efficiency of the available IP space. Since IPv6 has an exponentially higher number of IP addresses available, system administrators may reduce this practice. Subnetting has the side effect of reducing unnecessary web traffic. The result of less subnetting would result in the disadvantage of an increased traffic load on DNS servers.
Since IPv6 does not need or allow for NAT, a security feature existing in NAT does not apply to IPv6. NAT hides the internal network IP addresses and port numbers to not be visible to the outside world. The fact that IPv6 does not allow for this could be considered a disadvantage. This disadvantage is arguable since the hiding of internal network IP addresses is not regarded as a robust security feature.
As mentioned, IPv6 uses SLAAC to assign IP addresses automatically. Using SLAAC, the IPv6 end nodes choose their own IP addresses. An issue arises because the DNS servers still need to have reverse DNS records for the IP selected using SLAAC, but these records are not available to the DNS servers (Internet Society, 2014). Several options have been recommended and implemented for overcoming this issue, so this disadvantage is no longer relevant.
How IPv6 May change the way networks use DNS
The IPv6 advantages of eliminating NAT and increased IP space, along with the proliferation of new connected IoT devices, will lead to massively increased traffic to DNS servers. This increase will likely require the DNS server infrastructure to scale up to meet the demand. More processing power and storage will be required. The DNS hierarchy can is a tree that consists of managed zones with root servers at the top. Due to limitations in IPv4, there are only 13 root server addresses, but there are over 600 different root servers distributed across the world. The increase in internet traffic and the removal of the limitations of IPv4 may also lead to the implementation of additional root server addresses.
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Kralicek, E. (2016). Accidental SysAdmin Handbook, Sybex.
Liu, C. (2011). DNS and BIND on IPv6, O’Reilly
Panek, C. (2020). Networking Fundamentals, Springer Nature.
Pete, L. (2004). IPv6: Theory, protocol, and practice 2nd ed) Morgan Kaufmann
DNS considerations for IPv6. (2014, June 14). Internet Society. https://www.internetsociety.org/resources/deploy360/2014/dns-considerations-for-ipv6/
IPv6 address representation and address types. (2017, October 3). Cisco Press. https://www.ciscopress.com/articles/article.asp?p=2803866
Multicast protocols user guide (2021, January 13). Juniper. https://www.juniper.net/documentation/us/en/software/junos/multicast/topics/concept/multicast-ip-overview.html