Internetwork Packet Exchange (IPX) is the
network layer
In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers.
Functions
The network layer provides the means of transfe ...
protocol
Protocol may refer to:
Sociology and politics
* Protocol (politics), a formal agreement between nation states
* Protocol (diplomacy), the etiquette of diplomacy and affairs of state
* Etiquette, a code of personal behavior
Science and technology
...
in the
IPX/SPX
IPX/SPX stands for Internetwork Packet Exchange/Sequenced Packet Exchange. IPX and SPX are networking protocols used initially on networks using the (since discontinued) Novell NetWare operating systems. They also became widely used on netwo ...
protocol suite
The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. Some of these terms are used interchangeably but strictly speaking, the ''suite'' is the definition of the communication protoc ...
. IPX is derived from
Xerox Network Systems
Xerox Network Systems (XNS) is a computer networking protocol suite developed by Xerox within the Xerox Network Systems Architecture. It provided general purpose network communications, internetwork routing and packet delivery, and higher level f ...
'
IDP. It also has the ability to act as a
transport layer
In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end ...
protocol.
The IPX/SPX protocol suite was very popular through the late 1980s and mid-1990s because it was used by
Novell
Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare.
Under the lead ...
NetWare
NetWare is a discontinued computer network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, using the IPX network protocol.
The original NetWare product in 19 ...
, a
network operating system
A network operating system (NOS) is a specialized operating system for a network device such as a router, switch or firewall.
Historically operating systems with networking capabilities were described as network operating systems, because they al ...
. Due to Novell NetWare's popularity, IPX became a prominent protocol for
internetworking
Internetworking is the practice of interconnecting multiple computer networks, such that any pair of hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology. The resulting system of interco ...
.
A big advantage of IPX was a small
memory footprint
Memory footprint refers to the amount of main memory that a program uses or references while running.
The word footprint generally refers to the extent of physical dimensions that an object occupies, giving a sense of its size. In computing, the ...
of the IPX driver, which was vital for
DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicat ...
and
Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
up to
Windows 95
Windows 95 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of operating systems. The first operating system in the 9x family, it is the successor to Windows 3.1x, and was released to manufacturin ...
due to the limited size at that time of
conventional memory
In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory directly addressable by the processor for use by the operating system ...
. Another IPX advantage is easy configuration of its client computers. However, IPX does not scale well for large networks such as the Internet. As such, IPX usage decreased as the boom of the
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
made
TCP/IP
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
nearly universal.
Computers and networks can run multiple
network protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...
s, so almost all IPX sites also run TCP/IP, to allow Internet connectivity. It is also possible to run later Novell products without IPX, with the beginning of full support for both IPX and TCP/IP by NetWare version 5 in late 1998.
Description
A big advantage of IPX protocol is its little or no need for configuration. In the time when protocols for
dynamic host configuration did not exist and the
BOOTP
The Bootstrap Protocol (BOOTP) is a computer networking protocol used in
Internet Protocol networks to automatically assign an IP address to network devices from a configuration server. The BOOTP was originally defined in RFC 951.
While some part ...
protocol for centralized assigning of addresses was not common, the IPX network could be configured almost automatically. A client computer uses the
MAC address
A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking techno ...
of its network card as the node address and learns what it needs to know about the network topology from the servers or
routers – routes are propagated by
Routing Information Protocol
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from sourc ...
, services by
Service Advertising Protocol The Service Advertising Protocol (SAP) is included in the Internetwork Packet Exchange (IPX) protocol. SAP makes the process of adding and removing services on an IPX internetwork dynamic. SAP was maintained by Novell
Novell, Inc. was an Ameri ...
.
A small IPX network administrator had to care only
* to assign all servers in the same network the same network number,
* to assign different network numbers to different frame formats in the same network,
* to assign different network numbers to different interfaces of servers with multiple network cards (Novell
NetWare
NetWare is a discontinued computer network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, using the IPX network protocol.
The original NetWare product in 19 ...
server with multiple network cards worked automatically as a router),
* to assign different network numbers to servers in different interconnected networks,
* to start router process on nodes with multiple network cards in more complex networks.
IPX packet structure
Each IPX packet begins with a header with the following structure:
The Packet Type values are:
IPX addressing
An IPX address has the following structure:
Network number
The network number allows to address (and communicate with) the IPX nodes which do not belong to the same network or ''cabling system''. The cabling system is a network in which a
data link layer
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...
protocol can be used for communication. To allow communication between different networks, they must be connected with IPX
routers. A set of interconnected networks is called an internetwork. Any
Novell NetWare
NetWare is a discontinued computer network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, using the IPX network protocol.
The original NetWare product in 19 ...
server may serve as an IPX router. Novell also supplied stand-alone routers. Multiprotocol routers of other vendors often support IPX routing. Using different
frame formats in one cabling system is possible, but it works similarly as if separate cabling systems were used (i.e. different network numbers must be used for different frame formats even in the same cabling system and a router must be used to allow communication between nodes using different frame formats in the same cabling system).
* Logical networks are assigned a unique 32-bit address in the range 0x1 to 0xFFFFFFFE (
hexadecimal
In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
).
* Hosts have a 48-bit node address, which is by default set to the 6 bytes of the network interface card
MAC address
A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking techno ...
. Network addresses, which exist in addition to the node address, but are not part of the MAC layer, are assigned only if an IPX router is present or by manual configuration in the network. The network address covers every network participant that can talk to another participant without the aid of an IPX router. In combination, both network and node address form a 80 bit unique identifier for each IPX node across connected logical networks. The node number itself is unique to the logical network only.
* Network number 00:00:00:00 refers to the current network, and is also used during router discovery. It's also the default in case no router is present, but can be changed by manual configuration, depending on the IPX implementation.
* Broadcast network number is FF:FF:FF:FF.
Node number
The node number is used to address an individual computer (or more exactly, a network interface) in the network. Client stations use its network interface card
MAC address
A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking techno ...
as the node number.
The value FF:FF:FF:FF:FF:FF may be used as a node number in a destination address to
broadcast
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...
a packet to "all nodes in the current network".
Socket number
The socket number serves to select a process or application in the destination node.
The presence of a socket number in the IPX address allows the IPX to act as a
transport layer
In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end ...
protocol, comparable with the
User Datagram Protocol
In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...
(UDP) in the
Internet protocol suite
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
.
Comparison with IP
The IPX network number is conceptually identical to the network part of the
IP address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
(the parts with
netmask
A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. The practice of dividing a network into two or more networks is called subnetting.
Computers that belong to the same subnet are addressed with an identical ...
bits set to 1); the node number has the same meaning as the bits of IP address with netmask bits set to 0. The difference is that the boundary between network and node part of address in IP is variable, while in IPX it is fixed. As the node address is usually identical to the MAC address of the network adapter, the
Address Resolution Protocol
The Address Resolution Protocol (ARP) is a communication protocol used for discovering the link layer address, such as a MAC address, associated with a given internet layer address, typically an IPv4 address. This mapping is a critical function ...
is not needed in IPX.
For
routing
Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...
, the entries in the IPX
routing table
In computer networking, a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with tho ...
are similar to IP routing tables; routing is done by network address, and for each network address a network:node of the next router is specified in a similar fashion an IP address/netmask is specified in IP routing tables.
There are three routing protocols available for IPX networks. In early IPX networks, a version of
Routing Information Protocol
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from sourc ...
(RIP) was the only available protocol to exchange routing information. Unlike RIP for
IP, it uses delay time as the main metric, retaining the hop count as a secondary metric. Since NetWare 3, the
NetWare Link Services Protocol NetWare Link Services Protocol (NLSP) is a routing protocol for Internetwork Packet Exchange based on the Intermediate-System-to-Intermediate-System (IS-IS) protocol developed by the International Organization for Standardization (ISO). NLSP enabl ...
(NLSP) based on
IS-IS
Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this b ...
is available, which is more suitable for larger networks.
Cisco
Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...
routers implement an IPX version of
EIGRP
Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary pr ...
protocol as well.
[{{Cite book , title = Troubleshooting Campus Networks: Practical Analysis of Cisco and LAN Protocols , first1 = Priscilla , last1 = Oppenheimer , first2 = Joseph , last2 = Bardwell , date = August 2002 , isbn = 978-0-471-21013-9 , publisher = John Wiley & Sons, Inc. , pages = 421–440]
Frame formats
IPX can be transmitted over Ethernet using one of the following 4 frame formats or encapsulation types:
*
802.3 (raw) encapsulation comprises an IEEE 802.3 frame header (destination MAC, source MAC, length) immediately followed by IPX data. It is used in legacy systems, and can be distinguished by the first two bytes of the IPX header always containing a value of 0xFFFF, which cannot be interpreted as valid LLC Destination and Source
Service Access Point A Service Access Point (SAP) is an identifying label for network endpoints used in Open Systems Interconnection (OSI) networking.
The SAP is a conceptual location at which one OSI layer can request the services of another OSI layer. As an example, ...
s in this location of the frame.
*
802.2 (LLC or Novell) comprises an IEEE 802.3 frame header (destination MAC, source MAC, length) followed by an
LLC header (
DSAP 0xE0,
SSAP 0xE0, control 0x03) followed by IPX data. The 0xE0 fields of the LLC header indicate "NetWare".
*
802.2 (
SNAP
Snap or SNAP may refer to:
Arts and entertainment
* ''Snap'', the original release title for the 2013 film ''Enter the Dangerous Mind''
*''Snap'' (TV series), a CITV programme
* ''The Stanly News and Press'', a newspaper in Albemarle, North Carol ...
) comprises an IEEE 802.3 frame header, an LLC header (DSAP 0xAA, SSAP 0xAA, control 0x03), a SNAP header (
OUI 0x000000, type 0x8137), and IPX data. The 0xAA fields of the LLC header indicate "SNAP", and the OUI 0x000000 in the SNAP header indicates an encapsulated
EtherType
EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the payload of the frame and is used at the receiving end by the data link layer to determine how the payload is processed. The same f ...
.
*
Ethernet II
In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload.
...
encapsulation comprises an Ethernet II frame header (destination MAC, source MAC,
EtherType
EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the payload of the frame and is used at the receiving end by the data link layer to determine how the payload is processed. The same f ...
0x8137) followed by IPX data.
In non-Ethernet networks only 802.2 and SNAP frame types are available.
References
External links
RFC 1132 - A Standard for the Transmission of 802.2 Packets over IPX Networks
Novell NetWare
Network layer protocols