IPX/SPX
From Wikipedia, the free encyclopedia
| The five layer TCP/IP model |
| 5. Application layer |
|
DHCP • DNS • FTP • HTTP • IMAP4 • IRC • NNTP • XMPP • MIME • POP3 • SIP • SMTP • SNMP • SSH • TELNET • BGP • RPC • RTP • RTCP • TLS/SSL • SDP • SOAP • L2TP • PPTP • … |
| 4. Transport layer |
| 3. Network layer |
| 2. Data link layer |
|
ATM • DTM • Ethernet • FDDI • Frame Relay • GPRS • PPP • ARP • RARP • … |
| 1. Physical layer |
|
Ethernet physical layer • ISDN • Modems • PLC • SONET/SDH • G.709 • Wi-Fi • … |
IPX/SPX stands for Internetwork Packet Exchange/Sequenced Packet Exchange. It is a networking protocol used by the Novell NetWare operating systems. Like UDP, IPX is a datagram protocol used for connectionless communications. IPX and SPX are derived from Xerox Network Services' IDP and SPP protocols.
SPX is a transport layer protocol (layer 4 of the OSI Model) used in Novell Netware networks. The SPX layer sits on top of the IPX layer (layer 3 - the network layer) and provides connection-oriented services between two nodes on the network. SPX is used primarily by client/server applications.
IPX and SPX both provide connection services similar to TCP/IP, with the IPX protocol having similarities to IP, and SPX having similarities to TCP. IPX/SPX was primarily designed for local area networks (LANs), and is a very efficient protocol for this purpose (typically its performance exceeds that of TCP/IP on a LAN). TCP/IP has, however, become the de facto protocol. This is in part due to its superior performance over wide area networks and the Internet (which uses TCP/IP exclusively), and also because TCP/IP is a more mature protocol, designed specifically with this purpose in mind.
Novell is largely responsible for the use of IPX as a popular computer networking protocol due to their dominance in the network operating system software market (with Novell Netware) from the late 1980s through to the mid-1990s.
Because of IPX/SPX's prevalence in LANs in the 1990's, Microsoft added support for the protocols into Windows' networking stack, starting with Windows for Workgroups and Windows NT. Microsoft even named their implementation "NWLink", implying that the inclusion of the layer 3/4 transports provided NetWare connectivity. In reality, the protocols were supported as a native transport for Windows' SMB/NetBIOS, and NetWare connectivity required additional installation of an NCP client (Microsoft provided a basic NetWare client with Windows 95 and later, but it was not automatically installed, and initially only supported NetWare bindery mode). NWLink is still provided with Windows (up to and including Windows 2003) (However it is neither included on nor supported in Windows Vista, Novell will be starting a closed beta in March 2007), but its use is strongly discouraged, because it cannot be used for Windows networking except as a transport for NetBIOS, which is deprecated.
For the most part, Novell's 32-bit Windows client software have eschewed NWLink for an alternative developed by Novell, although some versions permit use of Microsoft's IPX/SPX implementation (with warnings about potential incompatibility).
IPX usage has declined in recent years as the rise of the Internet has made TCP/IP ubiquitous. Novell's initial attempt to support TCP/IP as a client protocol, called NetWare/IP, simply "tunnelled" IPX within IP packets, allowing NetWare clients and servers to communicate over pure TCP/IP networks. However, due to complex implementation, and a significant loss in performance due to the tunnelling overhead, NetWare/IP was largely ignored except as a mechanism to route IPX through TCP/IP-only routers and WAN links. NetWare 5.x introduced native support for NCP over TCP/IP, which is now the preferred configuration.
Both Microsoft and Novell have provided support (through Proxy Server/ISA Server and BorderManager, respectively) for IPX/SPX as an intranet protocol to communicate through a firewall. This allows a machine using client software to access the Internet without having TCP/IP installed locally; the client software emulates a native TCP/IP stack and provides WinSock support for local applications (e.g. web browsers), but actually communicates with the firewall over IPX/SPX. In addition to simplifying migration for legacy IPX LANs, this provides a measure of security, as the use of the IPX protocol on the internal network provides a natural barrier against intruders, should the firewall be compromised.
One area where IPX remains useful is to sidestep VPNs that force all TCP/IP traffic to traverse the VPN, preventing any access to local resources such as printers and shared disks.
