Internetwork Packet Exchange

IPX Internetwork Packet eXchange, is a system developed by Novell computer network protocol. It is derived from the IDP Protocol Xerox Network Services ( XNS ), and was primarily for the network operating system ( NOS), NetWare used.

IPX is a connectionless, proprietary protocol with routing capability, which is functionally equivalent to the IP or UDP. The building on IPX protocol SPX ( Sequenced Packet Exchange) realized in analogy with TCP, the TCP / IP protocol family the secure, connection-oriented communication. However, using the server functions of NetWare IPX only, the security features are in the NetWare Core Protocol (NCP ) itself independently of SPX implemented. By using the Service Advertising Protocol (SAP), it is possible to find the services provided within an IPX network.

With increasing penetration of the Internet in the mid- 1990s, the direct support of TCP / IP in Novell NetWare and the declining market share of NetWare IPX / SPX increasingly lost over TCP / IP in importance. It is now rarely used, although it is still supported by both NetWare and clients such as Windows or Linux. Microsoft provided a support from Windows Vista, so Windows XP is the last Windows for the time being for home with IPX support.

The protocol in the OSI model

The protocol in the OSI model (see in comparison to the TCP / IP reference model, OSI model):


IPX was developed from the beginning with respect to the resulting also at Xerox Ethernet. IPX uses binary addresses, consisting of a 32 -bit long network number and a 48 bit long host address ( the MAC address of the interface ) and a 16 -bit long socket number, which corresponds approximately to the port address in TCP or UDP. IPX therefore has a much larger address space than IP version 4, where network and host are encoded together in 32 bits.

Construction of data packets

An IPX packet consists of the 30 -byte IPX header followed by the payload:

  • The 16 -bit checksum field is always set to 0xFFFF, as checksums for IPX are not supported.
  • The 16 -bit long packet length field contains the total size of the packet (header and payload ).
  • The 8 -bit number in transport box Control is the hop counter that is incremented when going through a router. If he eventually reaches 16, the packet is usually discarded ( see purpose TTL).
  • This 8 -bit field type describes the embedded protocol (encapsulated protocol):
  • Fields Source Network / Node / Socket and Destination Network / Node / Socket contain the corresponding components of sender or recipient address, the following socket numbers are defined:

The data area has a variable length. 1536 bytes for Ethernet, for example, minus the 30 bytes of the IPX header data area itself - Since IPX packets are not fragmented by default, the maximum packet size depends on the network medium from


A network station generates its own address from its MAC address and an administrator-configured network number. ( In IPX is not intended as opposed to IP, that on a physical network segment multiple network numbers are used side by side ).

Packets within the local network (same network number ) will be sent directly to the included MAC address. Detects a participant a destination in a foreign network, it asks by RIP broadcast by a competent router to the MAC address it sends the packet then. The resulting router addresses are cached locally. 's Broadcast routers themselves at regular intervals ( default one minute) lists of network numbers that can be reached through it, where RIP packets more remote router is not forwarded separately, but are summarized.

RIP generates current broadcast traffic and is therefore inefficient over WAN connections and dialup connections with automatic connection establishment / degrading only with difficulty be used. It was therefore replaced by a link-state routing protocol called NLSP, but the basic RIP functions for router discovery remained backward compatible.

Search services ( service advertising)

Analogous to the determination of router addresses with RIP manages SAP with a combination of regular broadcasts and broadcast requests a list of the network of offered services. These lists are summarized in routers.