Editing Internetwork Packet Exchange (section)

==IPX addressing==

An IPX address has the following structure:

{|class=wikitable style="text-align:left;"
|-
! Octets !! Field
|-
| 4 || Network number
|-
| 6 || Node number
|-
| 2 || Socket number
|}

===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]] protocol can be used for communication. To allow communication between different networks, they must be connected with IPX [[Router (computing)|routers]]. A set of interconnected networks is called an '''internetwork'''. Any [[Novell NetWare]] server may serve as an IPX router. Novell also supplied stand-alone routers. Other vendors ' multiprotocol routers often support IPX routing. Using different [[#Frame Formats|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]]).
* Hosts have a 48-bit node address, which is by default set to the 6 bytes of the network interface card [[MAC address]]. 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 an 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]] 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 address|broadcast]] 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]] protocol, comparable with the [[User Datagram Protocol]] (UDP) in the [[Internet protocol suite]].

{|class=wikitable style="text-align:left;"
|-
! Socket number !! Protocol
|-
| 0x0001–0x0BB8 || Registered by [[Xerox]]
|-
| 0x0001 || Routing Information Packet
|-
| 0x0002 || Echo Protocol Packet
|-
| 0x0003 || Error Handling Packet
|-
| 0x0020–0x003F || Experimental
|-
| 0x0BB9–0xFFFF || Dynamically Assigned
|-
| 0x0451 || [[NetWare Core Protocol]] (NCP – used by [[Novell NetWare]] servers)
|-
| 0x0452 || [[Service Advertising Protocol]] (SAP)
|-
| 0x0453 || [[Routing Information Protocol]] (RIP)
|-
| 0x0455 || [[NetBIOS]]
|-
| 0x0456 || Diagnostic Packet
|-
| 0x0457 || Serialization Packet (used for NCP as well)
|-
| 0x4000–0x4FFF || Dynamically Assigned Socket Numbers 
|-
| 0x4003 || Used by [[Novell NetWare]] Client
|-
| 0x8000–0xFFFF || Statically Assigned Socket Numbers
|-
| 0x8060 || [[Logical Link Control|LLC]]<ref name="RFC1132" />
|-
| 0x9091 || [[Transmission Control Protocol|TCP]] over IPXF
|-
| 0x9092 || [[User Datagram Protocol|UDP]] over IPXF
|-
| 0x9093 || IPXF, IPX Fragmentation Protocol
|}

===Comparison with IP===
The IPX network number is conceptually identical to the network part of the [[IP address]] (the parts with [[netmask]] 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]] is not needed in IPX.

For [[routing]], the entries in the IPX [[routing table]] 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]] (RIP) was the only available protocol to exchange routing information. Unlike RIP for [[Internet Protocol|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]] (NLSP) based on [[IS-IS]] is available, which is more suitable for larger networks. [[Cisco]] routers implement an IPX version of [[Enhanced Interior Gateway Routing Protocol|EIGRP]] protocol as well.<ref>{{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}}</ref>