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If you are using Internet or almost any computer network you will likely using IPv4 packets. IPv4 uses 32-bit source and destination address fields. We are actually running out of addresses but have not fear, the Internet Engineering Task Force (IETF) is here with IPv6.

The IPv6 packet (Fig. 1) doesn't look much like its IPv4 (Fig. 2) cousin, except for the leading version field. The IPv6 address fields are 128-bits. The larger address space is one reason to migrate to IPv6 but there are many more differences that give IPv6 an advantage. For example, the header checksum field has been eliminated because transport reliability has gone up and its overhead was unnecessary.

The movement to IPv6 on a global scale is inevitable. It has been more of an issue of getting the infrastructure in place to make the move to cause the minimal number of problems. It is possible for IPv4 and IPv6 subnets to exchange traffic but there are issues that vary depending upon the network configuration and the type of network traffic.

Here are some of the major differences between IPv4 and IPv6. Both standards are extensive and many features are less obvious and important for only some environments.

IPv4/IPv6 Differences




Address 32 bits (4 bytes)
128 bits (16 bytes)
Packet size 576 bytes required, fragmentation optional 1280 bytes required without fragmentation
Packet fragmentation Routers and sending hosts Sending hosts only
Packet header Does not identify packet flow for QoS handling Contains Flow Label field that specifies packet flow for QoS handling
Includes a checksum Does not include a checksum
Includes options
up to 40 bytes
Extension headers used for optional data
DNS records Address (A) records,
maps host names
Address (AAAA) records,
maps host names
Pointer (PTR) records,
Pointer (PTR) records,
IP6.ARPA DNS domain
Address configuration Manual or via DHCP Stateless address autoconfiguration (SLAAC) using Internet Control Message Protocol version 6 (ICMPv6) or DHCPv6
IP to MAC resolution broadcast ARP Multicast Neighbor Solicitation
Local subnet group management Internet Group Management Protocol (IGMP) Multicast Listener Discovery (MLD)
Broadcast Yes No
Multicast Yes Yes
IPSec optional, external required