Internetwork Packet Exchange IPX
Internetwork Packet Exchange (IPX) is a legacy Network-layer (Layer 3) protocol that served as the primary communication backbone for local area networks (LANs) running the Novell NetWare operating system during the late 1980s and 1990s. Derived from Xerox Network Systems’ IDP, it is a connectionless, datagram-based protocol that provides best-effort delivery of routed packets, handling logical addressing and path determination.
Architecture and Addressing
80 bits (10 bytes) make up the special hierarchical addressing method used by IPX. Three primary parts make up this address:
- Network Number (32 bits): A hexadecimal address (0x1 to 0xFFFFFFFE) that a network administrator assigns to a logical network segment is known as the network number (32 bits).
- Node Number (48 bits): a unique way to identify a particular network interface. By default, this is the network card’s hardware MAC address.
- Socket Number (16 bits): Like ports in TCP/IP, this number is used to choose a particular process or application within the destination node.
As the IPX address incorporates the hardware MAC address directly, the protocol does not require an Address Resolution Protocol (ARP). As a result, clients could automatically learn network topology from routers or servers and obtain their addresses from their hardware, enabling a “Plug-and-Play” or zero-configuration experience.
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The IPX/SPX Protocol Suite
Rather than operating alone, IPX served as the basis for a group of protocols that oversaw various networking functions:
- Sequenced Packet Exchange (SPX): A dependable, connection-oriented delivery system that guarantees packets are received in the right order is called Sequenced Packet Exchange (SPX).
- Service Advertising Protocol (SAP): Every 60 seconds, servers use SAP to announce the services they offer, such as file or print sharing.
- Routing Information Protocol (RIP): A distance-vector protocol called Routing Information Protocol (RIP) is used to share routing data. The key statistic, “ticks” (1/18th of a second delay), is used instead of hop counts, which are used as a tiebreaker in the IP version of RIP.
- NetWare Core Protocol (NCP): Specifically designed for file and print sharing between NetWare clients and servers, the “workhorse” protocol is called NetWare Core Protocol (NCP).
Encapsulation and Framing
There are four different frame types that IPX can use while being sent over Ethernet:
- 802.3 (Raw): Used in legacy systems; it places IPX data immediately after the IEEE 802.3 header.
- 802.2 (LLC): Often used by NetWare 3.12 and 4.x, incorporating a Logical Link Control header.
- 802.2 (SNAP): Includes a Sub-Network Access Protocol header.
- Ethernet II (ARPA): Typically used in environments running both IPX and TCP/IP.
Cisco IOS Implementation and Verification
To route IPX along with other protocols, Cisco routers can function as multiprotocol devices. The ipx routing procedure must be enabled globally, and an interface must be assigned a network number using ipx network [number].
The following are typical commands for monitoring and troubleshooting:
- show ipx route: The IPX routing table can be seen by using the show ipx route function.
- show ipx servers: All network services found using SAP are listed in the “show ipx servers” section.
- show ipx interface: Displays the IPX attributes and status for a given interface.
- debug ipx routing activity: RIP update packets are seen in real time when debugging IPX routing activities.
Historical Significance and Decline
Because of its modest memory footprint which was essential for DOS and early Windows and its user-friendliness in small-to-medium LANs, IPX was popular at its height. But it was no longer in use for a number of reasons:
- Scaling Issues: Due to their “flat” nature, IPX addresses did not have the hierarchical structure required for international networks such as the Internet.
- High Overhead: The “chatty” nature of SAP broadcasts could overload slower wide-area network (WAN) lines, resulting in high overhead.
- Universal Adoption of TCP/IP: The industry moved toward vendor-independent open standards as the web expanded, leading to the widespread adoption of TCP/IP.
Although it is mostly out of usage now, IPX is still used in some vintage industrial systems and for retro gaming (by tunneling IPX across contemporary networks using emulators like DOSBox). Keep in mind that IPX, a contemporary telecommunications model for mobile roaming, should not be confused with this outdated protocol.
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