Comparison of IPv4 and IPv6

You might wonder how IPv6 differs from IPv4. You can use this table to quickly look up different concepts, IP functions, and the use of IP addresses in Internet protocols between IPv4 and IPv6.

You can select an attribute from this list to link to the comparison in the table.

Description IPv4 IPv6
Address 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 lifetime Generally, this is not an applicable concept for IPv4 addresses, except for addresses assigned using DHCP. IPv6 addresses have two lifetimes: preferred and valid, with the preferred lifetime always <= valid.

After the preferred lifetime expires, the address is not to be used as a source IP address for new connections if an equally good preferred address is available. After the valid lifetime expires, the address is not used (recognized) as a valid destination IP address for incoming packets or used as a source IP address.

Some IPv6 addresses have, by definition, infinite preferred and valid lifetimes; for example link-local (see address scope).

Address mask Used to designate network from host portion. Not used (see address prefix).
Address prefix Sometimes used to designate network from host portion. Sometimes written as /nn suffix on presentation form of address. Used to designate the subnet prefix of an address. Written as /nnn (up to 3 decimal digits, 0 <= nnn <= 128) suffix after the print form. An example is fe80::982:2a5c/10, where the first 10 bits comprise the subnet prefix.
Address Resolution Protocol (ARP) ARP is used by IPv4 to find a physical address, such as the MAC or link address, associated with an IPv4 address. IPv6 embeds these functions within IP itself as part of the algorithms for stateless autoconfiguration and neighbor discovery using Internet Control Message Protocol version 6 (ICMPv6). Hence, there is no such thing as ARP6.
Address scope For unicast addresses, this concept does not apply. There are designated private address ranges and loopback. Outside of that, addresses are assumed to be global.

In IPv6, address scope is part of the architecture. Unicast addresses have two defined scopes, including link-local and global; and multicast addresses have 14 scopes. Default address selection for both source and destination takes scope into account.

A scope zone is an instance of a scope in a particular network. As a consequence, IPv6 addresses sometimes must be entered or associated with a zone ID. The syntax is %zid where zid is a number (typically small) or a name. The zone ID is written after the address and before the prefix. For example, 2ba::1:2:14e:9a9b:c%3/48.

Address types IPv4 addresses are categorized into three basic types: unicast address, multicast address, and broadcast address. IPv6 addresses are categorized into three basic types: unicast address, multicast address, and anycast address. See IPv6 address types for descriptions.
Communications trace Communications trace is a tool to collect a detailed trace of TCP/IP (and other) packets that enter and leave the system. Same support for IPv6.
Configuration 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. (See API getnameinfo()–Get Name Information for Socket Address for details.)

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. The IBM i implementation of DHCP does not support IPv6. However, ISC DHCP server implementation can be used.
File Transfer Protocol (FTP) FTP allows you to send and receive files across networks. Same support for IPv6.
Fragments When a packet is too big for the next link over which it is to travel, it can be fragmented by the sender (host or router). For IPv6, fragmentation can only occur at the source node, and reassembly is only done at the destination node. The fragmentation extension header is 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.
IBM Navigator for i support IBM Navigator for i provides a complete configuration solution for TCP/IP. Same support for IPv6.
Interface The conceptual or logical entity used by TCP/IP to send and receive packets and always closely associated with an IPv4 address, if not named with an IPv4 address. Sometimes referred to as a logical interface.

IPv4 interfaces can be started and stopped independently of each other and independently of TCP/IP using the STRTCPIFC and ENDTCPIFC commands and using IBM Navigator for i.

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.

Internet Group Management Protocol (IGMP) IGMP is used by IPv4 routers to find hosts that want traffic for a particular multicast group, and used by IPv4 hosts to inform IPv4 routers of existing multicast group listeners (on the host). IGMP is replaced by MLD (multicast listener discovery) protocol for IPv6. MLD does essentially what IGMP does for IPv4, but uses ICMPv6 by adding a few MLD-specific ICMPv6 type values.
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.
IP header options Various options might accompany an IP header (before any transport header). The IPv6 header has no options. Instead, IPv6 adds additional (optional) extension headers. The extension headers are AH and ESP (unchanged from IPv4), hop-by-hop, routing, fragment, and destination. Currently, IPv6 supports some extension headers.
IP header protocol byte The protocol code of the transport layer or packet payload (for example, ICMP). The type of header immediately following the IPv6 header. Uses the same values as the IPv4 protocol field. But the architectural effect is to allow a currently defined range of next headers, and is easily extended. The next header will be a transport header, an extension header, or ICMPv6.
IP header Type of Service byte Used by QoS and differentiated services to designate a traffic class. Uses different codes to designate an IPv6 traffic class. Currently, IPv6 does not support TOS.
LAN connection LAN connection is used by an IP interface to get to the physical network. Many types exist; for example, token ring and 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.
Layer Two Tunnel Protocol (L2TP) L2TP can be thought of as virtual PPP, and works over any supported line type. Same support for IPv6.
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.
Maximum transmission unit (MTU) Maximum transmission unit of a link is the maximum number of bytes that a particular link type, such as Ethernet or modem, supports. For IPv4, 576 is the typical minimum. IPv6 has a lower boundary limit on MTU of 1280 bytes. That is, IPv6 does not fragment packets below this limit. To send IPv6 over a link with an MTU of less than 1280 bytes, the link-layer must transparently fragment and defragment the IPv6 packets.
Netstat Netstat is a tool to look at the status of TCP/IP connections, interfaces, or routes. Available using IBM Navigator for i and the character-based interface. Same support for IPv6.
Network address translation (NAT) Basic firewall functions integrated into TCP/IP, configured using IBM Navigator for i. Currently, NAT does not support IPv6. More generally, IPv6 does not require NAT. The expanded address space of IPv6 eliminates the address shortage problem and enables easier renumbering.
Network table On IBM Navigator for i, a configurable table that associates a network name with an IP address without mask. For example, host Network 14 and IP address Currently, no changes are made to this table for IPv6.
Node info query Does not exist. A simple and convenient network tool that should work like ping, except with content: an IPv6 node may query another IPv6 node for the target's DNS name, IPv6 unicast address, or IPv4 address. Currently, not supported.
Open Shortest Path First (OSPF) OSPF is a router protocol used within larger autonomous system networks in preference to RIP. Same support for IPv6.
Packet filtering Packet filtering is the basic firewall functions integrated into TCP/IP. It is configured by using IBM Navigator for i. Packet filtering does not support IPv6.
Packet forwarding

The IBM i TCP/IP stack can be configured to forward IP packets that it receives for nonlocal IP addresses. Typically, the inbound interface and outbound interface are connected to different LANs.

Packet forwarding has limited support for IPv6. The IBM i TCP/IP stack does not support neighbor discovery as a router.

PING 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.
Point-to-Point Protocol (PPP) PPP supports dialup interfaces over various modem and line types. Same support for IPv6.
Port restrictions IBM Navigator for i allows a customer to configure a selected port number or port-number ranges for TCP or User Datagram Protocol (UDP) so that they are only available for a specific profile. Port restrictions for IPv6 are identical to those available in IPv4.
Ports TCP and UDP have separate port spaces, each identified by port numbers in the range 1-65535. For IPv6, ports work the same as IPv4. Because these are in a new address family, there are now four separate port spaces. For example, there are two TCP port 80 spaces to which an application can bind, one in AF_INET and one in AF_INET6.
Private and public addresses All IPv4 addresses are public, except for three address ranges that have been designated as private by IETF RFC 1918: 10.*.*.* (10/8), through (172.16/12) , and 192.168.*.* (192.168/16). Private address domains are commonly used within organizations. Private addresses cannot be routed across the Internet. IPv6 has an analogous concept, but with important differences.

Addresses are public or temporary, previously termed anonymous. See RFC 3041. Unlike IPv4 private addresses, temporary addresses can be globally routed. The motivation is also different; IPv6 temporary addresses are meant to shield the identity of a client when it initiates communication (a privacy concern). Temporary addresses have a limited lifetime, and do not contain an interface identifier that is a link (MAC) address. They are generally indistinguishable from public addresses.

IPv6 has the notion of limited address scope using its designed scope designations (see address scope).

Protocol table In IBM Navigator for i, the protocol table is a configurable table that associates a protocol name with its assigned protocol number; for example, UDP, 17. The system is shipped with a small number of entries: IP, TCP, UDP, ICMP. The table can be used with IPv6 without change.
Quality of service (QoS) Quality of service allows you to request packet priority and bandwidth for TCP/IP applications. Currently, the IBM i implementation of QoS does not support IPv6.
Renumbering Renumbering is done by manual reconfiguration, with the possible exception of DHCP. Generally, for a site or organization, renumbering is a difficult and troublesome process to avoid if possible. Renumbering is an important architectural element of IPv6, and is largely automatic, especially within the /48 prefix.
Route Logically, a mapping of a set of IP addresses (might contain only one) to a physical interface and a single next-hop IP address. IP packets whose destination address is defined as part of the set are forwarded to the next hop using the line. IPv4 routes are associated with an IPv4 interface, hence, an IPv4 address.

The default route is *DFTROUTE.

Conceptually, similar to IPv4. One important difference: IPv6 routes are associated (bound) to a physical interface (a link, such as ETH03) rather than an interface. One reason that a route is associated with a physical interface is because source address selection functions differently for IPv6 than for IPv4. See Source address selection.

Routing Information Protocol (RIP) RIP is a routing protocol supported by the routed daemon. Currently, RIP does not support IPv6.
Services table

On IBM i, a configurable table that associates a service name with a port and protocol; for example, service name FTP, port 21, TCP, and User Datagram Protocol (UDP).

A large number of well-known services are listed in the services table. Many applications use this table to determine which port to use.

No changes are made to this table for IPv6.
Simple Network Management Protocol (SNMP) SNMP is a protocol for system management. Same support for IPv6.
Sockets API These APIs are the way applications use TCP/IP. Applications that do not need IPv6 are not affected by sockets changes to support IPv6. IPv6 enhances sockets so that applications can now use IPv6, using a new address family: AF_INET6.

The enhancements have been designed so that existing IPv4 applications are completely unaffected by IPv6 and API changes. Applications that want to support concurrent IPv4 and IPv6 traffic, or IPv6-only traffic, are easily accommodated using IPv4-mapped IPv6 addresses of the form ::ffff:a.b.c.d, where a.b.c.d is the IPv4 address of the client.

The new APIs also include support for converting IPv6 addresses from text to binary and from binary to text.

See Using AF_INET6 address family for more information about sockets enhancements for IPv6.

Source address selection An application may designate a source IP (typically, using sockets bind()). If it binds to INADDR_ANY, a source IP is chosen based on the route. As with IPv4, an application can designate a source IPv6 address using bind(). Similarly to IPv4, it can let the system choose an IPv6 source address by using in6addr_any. But because IPv6 lines have many IPv6 addresses, the internal method of choosing a source IP is different.
Starting and stopping Use the STRTCP or ENDTCP command to start or end IPv4. IPv4 is always started when you run the STRTCP command to start TCP/IP. Use the STRIP6 parameter of the STRTCP or ENDTCP command to start or end IPv6. IPv6 might not be started when TCP/IP is started. IPv6 can be started independently at a later time.

Any IPv6 interfaces are automatically started if the AUTOSTART parameter is set to *YES (the default). IPv6 cannot be used or configured without IPv4. The IPv6 loopback interface, ::1, is automatically defined and activated when IPv6 is started.

Telnet Telnet allows you to log on and use a remote computer as though you were connected to it directly. Same support for IPv6.
Trace route Trace route is a basic TCP/IP tool to do path determination. Available using IBM Navigator for i and the character-based interface. Same support for IPv6.
Transport layers TCP, UDP, RAW. The same transports exist in IPv6.
Unspecified address Apparently, not defined, as such. Socket programming uses as INADDR_ANY. Defined as ::/128 (128 0 bits). It is used as the source IP in some neighbor discovery packets, and various other contexts, like sockets. Socket programming uses ::/128 as in6addr_any.
Virtual private network (VPN) Virtual private network (using IPsec) allows you to extend a secure, private network over an existing public network.

Same support for IPv6. See Virtual private network for details.