Comparison of IPv4 and IPv6 |

Comparison of IPv4 and IPv6

Basic Comparison





32 bits long (4 bytes). Address is composed of a network and a host portion, which depend on address class. Various address classes are defined: A, B, C, D, or E depending on initial few bits. The total number of IPv4 addresses is 4 294 967 296. The text form of the IPv4 address is nnn.nnn.nnn.nnn, where 0<=nnn<=255, and each n is a decimal digit. Leading zeros can be omitted. Maximum number of print characters is 15, not counting a mask.

128 bits long (16 bytes). Basic architecture is 64 bits for the network number and 64 bits for the host number. Often, the host portion of an IPv6 address (or part of it) will be derived from a MAC address or other interface identifier.

Depending on the subnet prefix, IPv6 has a more complicated architecture than IPv4.

The number of IPv6 addresses is 1028 (79 228 162 514 264 337 593 543 950 336) times larger than the number of IPv4 addresses. The text form of the IPv6 address is xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx, where each x is a hexadecimal digit, representing 4 bits. Leading zeros can be omitted. The double colon (::) can be used once in the text form of an address to designate any number of 0 bits. For example, ::ffff: is an IPv4-mapped IPv6 address.

Address allocation

Originally, addresses were allocated by network class. As address space is depleted, smaller allocations using Classless Inter-Domain Routing (CIDR) are made. Allocation has not been balanced among institutions and nations.

Allocation is in the earliest stages. The Internet Engineering Task Force (IETF) and Internet Architecture Board (IAB) have recommended that essentially every organization, home, or entity be allocated a /48 subnet prefix length. This will leave 16 bits for the organization to do subnetting. The address space is large enough to give every person in the world their own /48 subnet prefix length.

Address mask

Used to designate network from host portion.

Not used


You must configure a newly installed system before it can communicate with other systems; that is, IP addresses and routes must be assigned.

Configuration is optional, depending on functions required. IPv6 can be used with any Ethernet adapter and can be run over the loopback interface. IPv6 interfaces are self-configuring using IPv6 stateless autoconfiguration. You can also manually configure the IPv6 interface. So, the system will be able to communicate with other IPv6 systems that are local and remote, depending on the type of network and whether an IPv6 router exists.

Domain Name System (DNS)

Applications accept host names and then use DNS to get an IP address, using socket API gethostbyname().

Applications also accept IP addresses and then use DNS to get host names using gethostbyaddr().


For IPv4, the domain for reverse lookups is

Same support for IPv6. Support for IPv6 exists using AAAA (quad A) record type and reverse lookup (IP-to-name). An application may elect to accept IPv6 addresses from DNS (or not) and then use IPv6 to communicate (or not).

The socket API gethostbyname() only supports IPv4. For IPv6, a new getaddrinfo() API is used to obtain (at application choice) IPv6 only, or IPv4 and IPv6 addresses.


For IPv6, the domain used for reverse lookups is, and if they are not found then is used.

Dynamic Host Configuration Protocol (DHCP)

DHCP is used to dynamically obtain an IP address and other configuration information. IBM i supports a DHCP server for IPv4.

ISC DHCP server implementation can be used.

Host table

A configurable table that associates an Internet address with a host name (for example, for loopback). This table is used by the sockets name resolver, either before a DNS lookup or after a DNS lookup fails (determined by host name search priority).

Same support for IPv6.

Internet Control Message Protocol (ICMP)

Used by IPv4 to communicate network information.

Used similarly by IPv6; however, Internet Control Message Protocol version 6 (ICMPv6) provides some new attributes.

Basic error types remain, such as destination unreachable, echo request and reply. New types and codes are added to support neighbor discovery and related functions.

IP header

Variable length of 20-60 bytes, depending on IP options present.

Fixed length of 40 bytes. There are no IP header options. Generally, the IPv6 header is simpler than the IPv4 header.

LAN connection

LAN connection is used by an IP interface to get to the physical network. Many types exist; for example, Ethernet. Sometimes it is referred to as the physical interface, link, or line.

IPv6 can be used with any Ethernet adapters and is also supported over virtual Ethernet between logical partitions.

Loopback address

A loopback address is an interface with an address of 127.*.*.* (typically that can only be used by a node to send packets to itself. The physical interface (line description) is named *LOOPBACK.

The concept is the same as in IPv4. The single loopback address is 0000:0000:0000:0000:0000:0000:0000:0001 or ::1 (shortened version). The virtual physical interface is named *LOOPBACK.


PING is a basic TCP/IP tool to test reachability. Available using IBM Navigator for i and the character-based interface.

Same support for IPv6.

Source: IBM

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