IPv4 vs IPv6: What's the Difference?

July 18, 2018

The Internet Protocol (IP) is one of the most important communication protocols in the Internet Protocol Suite (IPS), which is used for routing and addressing packets for networking devices such as computers, laptops and fiber switches across a single network or a series of interconnected networks. There are currently two versions of Internet Protocol: IPv4 (IP version 4) and IPv6 (IP version 6). What do IPv4 and IPv6 mean? How to differentiate IPv6 and IPv4? Here, we will illustrate the definitions and differences between IPv4 and IPv6.

What Is IPv4?

IPv4 is the fourth version of IP, which establishes the rules for computer networks functioning on the principle of packet exchange. It can uniquely identify devices connected to the network through an addressing system. Whenever a device gets access to the Internet (whether it's a switch, PC, or other devices), it is assigned a unique, numerical IP address such as as shown below. The IPv4 uses a 32-bit address scheme allowing to store 2^32 addresses (4.19 billion addresses). The increasing end-users connected to the Internet leading to the exhaustion of IPv4 addresses. That’s also why the new Internet addressing system, IPv6, is being deployed to fulfill the need for more Internet addresses.

IPv4 Address Format.jpg

What Is IPv6?

IPv6 (Internet Protocol Version 6) was deployed in 1999 concerning that the demand for IP addresses would exceed the available supply. It allows communication and data transfer to take place over a network. IPv6 is a 128-bit IP address which supports 2^128 Internet addresses in total. The use of IPv6 not only solves the problem of limited network addresses resources but also resolves the barriers for multiple access devices to connect to the Internet. An IPv6 address could be written like this: 3ffe:1900:fe21:4545:0000:0000:0000:0000.

IPv6 Address Format.jpg

IPv4 vs IPv6

IPv4 and IPv6 are both addresses that are used to identify machines connected to a network. They are the same in principle but different in how they work. Then what are the differences between IPv4 and IPv6? The following descriptions will help you to find the answers.


Compared to IPv4, IPv6 increases the IP address from 32 bits to 128 bits to support larger address demands. It is estimated that there are 4x10^18 IPv6 addresses per square meter on the Earth's surface, so that IP addresses will not run out in the foreseeable future. The encoding of IPv6 addresses uses a hierarchy similar to CIDR, which simplifies the routing.

IP Header Format

There will be some redundant domains in the IPv4 header format, which has been either dropped or listed as extended headers in IPv6 addresses. Though the IP header size of IPv6 address is 4 times larger than IPv4 address, the IPv6 headers are only 2 times the size of IPv4. This greatly reduces the overhead of packet processing and header bandwidth.

Support for Options

The IPv4 options are placed in the header while IPv6 are put into a separate and extended header. The header will not be processed until you specify a router, which greatly improves the routing performance. The stringent requirements for option length have been relaxed by IPv6 (up to 40 bytes for IPv4 options) and new options will be introduced whenever you need it. Many of the new features of IPV6 are provided by options such as support for IP layer security (IPSEC), jumbogram, mobile IP and so on.

Network Security

For IPv4, the Internet Protocol Security (IPSec) is optional or requires payment support. While the IPSec is a required option for IPv6. Besides that, identity verification and data consistency have been added into IPv6 which greatly enhances security and confidentiality for your network.

Application Field

Nowadays, IPv6 has been successfully deployed in networks for many years. However, the application field of IPv4 is more extensive than IPv6. So how does this situation come into being? Obviously, there have been many issues after the deployment of IPv6, such as poor compatibility with existing infrastructure, difficulty in transitioning from IPv4 to IPv6 and so on. These have also led to the slow development of IPv6. Taking Google as an example, the following graph shows the percentage of users that access Google over IPv6 from 2009 to 2019. We can see from the table that IPv6 development speed is very slow in early stages. Until now, the proportion of users accessing Google via IPv6 is still not as good as IPv4.

IPv6 Adoption Trend Among Google Users.jpg

IPv6 vs IPv4 Specification

Differences IPv4 IPv6
Addressing Method A numeric address, and its binary bits are separated by a dot (.) An alphanumeric address whose binary bits are separated by a colon (:). It also contains hexadecimal.
Address Types Unicast, broadcast, and multicast. Unicast, multicast, and anycast.
Address Mask Use for the designated network from host portion. Not used.
Number of Header Fields 12 8
Length of Header Fields 20 40
Checksum Has checksum fields. No checksum fields.
Number of Classes Class A to E. Unlimited number of IP addresses.
Configuration IP addresses and routes must be assigned. Configuration is optional, depending on functions required.
VLSM Support Not Support
Fragmentation Done by sending and forwarding routes. Done by the sender.
Routing Information Protocol Supported by the routed daemon. RIP does not support IPv6. It uses static routes.
Network Configuration Manually or with DHCP. Autoconfiguration.
SNMP SNMP is a protocol used for system management. SNMP does not support IPv6.
Mobility & Interoperability Relatively constrained network topologies to which move restrict mobility and interoperability capabilities. IPv6 provides interoperability and mobility capabilities that are embedded in network devices.
DNS Records Pointer (PTR) records, IN-ADDR.ARPA DNS domain Pointer (PTR) records, IP6.ARPA DNS domain
IP to MAC resolution Broadcast ARP Multicast Neighbor Solicitation
Mapping Uses ARP(Address Resolution Protocol) to map to MAC address. Uses NDP(Neighbour Discovery Protocol) to map to MAC address.
Quality of Service (QoS) QoS allows you to request packet priority and bandwidth for TCP/IP applications. Currently, the IBM i implementation of QoS does not support IPv6.


From what we have discussed above, IPv6 is such an important step for the Internet and the movement from IPv4 to IPv6 on a global scale is inevitable. IPv6 not only enlarges addressing system and provides trillions of addresses to meet the internet demand for the foreseeable future, but also simplifies network operation and keeps costs down. This doesn’t mean that IPv4 will go away very soon. Perhaps one day, there will no longer be any IPv4 addresses in use, but that day is likely still in the distant future.

Related Article: IPv6 Address: Public vs Private


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