The Internet Protocol Version 4 (IPv4) is defined by IETF RFC 791. RFC 791 was published in 1981. Initial design of IPv4 did not anticipate the growth of internet and this created many issues, which proved IPv4 need to be changed. The main limitations of IPv4 are listed below.
• Scarcity of IPv4 Addresses: The IPv4 addressing system uses 32-bit address space. This 32-bit address space is further classified to usable A, B, and C classes. 32-bit address space allows for 4,294,967,296 IPv4 addresses, but the previous and current IPv4 address allocation practices limit the number of available public IPv4 addresses. Many addresses which are allocated to many companies were not used and this created scarcity of IPv4 addresses.
Because scarcity of IPv4 addresses, many organizations implemented NAT (Network Address Translation) to map multiple private IPv4 addresses to a single public IPv4 address. By using NAT (Network Address Translation) we can map many internal private IPV4 addresses to a public IPv4 address, which helped in conserving IPv4 addresses. But NAT (Network Address Translation) also have many limitations. NAT (Network Address Translation) do not support network layer security standards and it do not support the mapping of all upper layer protocols. NAT can also create network problems when two organizations which use same private IPv4 address ranges communicate. More servers, workstations and devices which are connected to the internet also demand the need for more addresses and the current statistics prove that public IPv4 address space will be depleted soon. The scarcity of IPv4 address is a major limitation of IPv4 addressing system.
• Security Related Issues: As we discussed before, RFC 791 (IPv4) was published in 1981 and the current network security threats were not anticipated that time. Internet Protocol Security (IPSec) is a protocol suit which enables network security by protecting the data being sent from being viewed or modified. Internet Protocol Security (IPSec) provides security for IPv4 packets, but Internet Protocol Security (IPSec) is not built-in and optional. Many IPSec implementations are proprietary.
• Address configuration related issues: Networks and also internet is expanding and many new computers and devices are using IP. The configuration of IP addresses (static or dynamic) should be simple.
• Quality of service (QoS): Quality of Service (QoS) is available in IPv4 and it relies on the 8 bits of the IPv4 Type of Service (TOS) field and the identification of the payload. IPv4 Type of Service (TOS) field has limited functionality and payload identification (uses a TCP or UDP port) is not possible when the IPv4 datagram packet payload is encrypted.