The IPX protocol is the main protocol used to transfer data from your UnixWare system to a NetWare server.
This topic provides a description of the protocols that make client-server commuNICations possible on NetWare networks. It explains packet structures defined by each protocol. It also describes how workstations, routers, and file servers transmit or receive packets.
If you plan to configure NetWare, you need a basic understanding of the NetWare protocols.
Most computer networks require information that is transferred between two nodes (workstations or servers) to be broken up into blocks, called packets. Sending information with packets makes a transfer between nodes and any intermediate nodes (bridges or routers) more manageable. In addition, each packet contains control information used for error checking, addressing, and other purposes. The protocols used on the network define the content of this control information.
In most cases, multiple protocols exist within a packet; each protocol defines a different portion of the control information for the packet, and the control information for each protocol serves a different purpose. When multiple protocols are used, the control information for the highest level protocol is first placed around the data, then the control information for each subsequent protocol in the protocol stack is added to the beginning or end of the packet. This is called enveloping.
To standardize the definition of protocols, several standards organizations were formed by governments and corporations. One of these groups, the International Standards Organization (ISO), has developed a model called the Open Systems Interconnection (OSI) model. This model specifies how protocols should be defined in the future. The OSI model separates the functions required for effective computer communications (such as error checking and addressing) into the following seven catagories or layers. These layers are Application, Presentation, Session, Transport, Network, Datalink, and Physical.
The protocols used by NetWare do not all correspond exactly to the OSI model definitions. NetWare uses a variety of protocols. Some were developed specifically for NetWare; some are used throughout the networking industry. The protocols required for communications between NetWare workstations and file servers are as follows:
MACs, such as 802.5 Token-Ring or 802.3 Ethernet, provide bit-level error checking through cyclic redundancy checking (CRC). This CRC which is added to every transmitted packet, assures that 99.9999 percent of the packets received are corruption free.
MAC protocols define the addressing for each node on a NetWare network. This addressing is provided by each network interface card.
The IPX protocol is a datagram, connectionless protocol that does not require an acknowledgement for each packet sent. Other NetWare protocols such as SPXII, SAP, RIP, and NCP are built on top of IPX.
The IPX protocol provides both IPX services and RIP services. As LAN drivers deliver packets to IPX, the IPX driver uses RIP to determine the route for packets outbound to other networks. Packets addressed to a local host are routed by IPX to the applications.
When setting up NetWare, you will need to configure your IPX internal LAN address and maximum hops, plus other information. See ``Managing NetWare protocols'' and ``Managing the server'' for more information.
IPX delivers packets using a 12-byte network address, which consists of three address components:
| 01010393. | 0123456789ab. | 0451 |
|---|---|---|
| Net | Node | Socket |
The SPXII is a connection-oriented, reliable, sequenced transport protocol. This protocol provides message-level service (for reliability) rather than packet-level service.
SPXII also provides flow control which regulates the speed with which packets are sent and received by both sending and receiving processes.
As a message service, SPXII provides enhanced throughput. This protocol reduces the amount of traffic on the wire by negotiating for large packets and reducing the number of acknowledgements.
Applications using SPXII do not need to determine packet size. The SPXII driver handles packet size for the application.
When setting up NetWare, you may want to turn on SPXII and enter other information such as the maximum number of SPXII connections and sockets for your network. See ``Managing NetWare protocols''.
The NVT2 service establishes terminal connections between DOS workstations and UNIX systems over SPXII.
NVT2 servers advertise remote login service and listen for SPX connection requests on the advertised socket. The NVT client then sends connection requests to the advertised socket.
Since NVT2 uses SPXII and each NVT2 connection requires a server SPXII connection, the maximum allowed SPXII connections which you specify in the ``NetWare Setup'' window should be at least 100.
With UnixWare, the NVT2 server uses the Service Access Facility (SAF-configured) listener to handle connect requests and the SAP daemon to handle advertising. When NVT2 is turned on in the ``NetWare Setup'' window, a script registers the SAF listener process on the NVT2 socket and NetWare Protocol Stack Daemon (NPSD) informs the SAP daemon to advertise NVT2. See ``Managing NetWare protocols'' or the nwcm(1Mipx) manual page for more information on NVT2.
If SPXII should go down normally, NVT2 will go down and come back up when SPXII comes back up.
If SPXII goes down abnormally (such as a crash), NVT2 will go down and come back up, but the service will remain registered with SAF and will be invalid. In this case, the protocol stacks must be brought back up manually.
The RIP allows routing information exchange on a NetWare internetwork. The single packet structure defined by the RIP allows the following exchanges of information:
The SAP allows service-providing nodes such as file servers, print servers, gateway servers, and client workstations to advertise services and addresses. The SAP makes adding and removing services on an internetwork dynamic. As servers are booted, they advertise services to other nodes through the SAP; when they are brought down, they use the SAP to indicate that services are no longer available.
Through the SAP, clients on the network can determine what services are available on the network, and obtain the internetwork address of the nodes where they can access those services. This is an important function, since a workstation cannot initiate a session with a file server without the server address.
A gateway server, for instance, will broadcast a SAP packet periodically (usually every 60 seconds, the period defined for all servers advertising with the SAP) onto the network segment to which it is connected. The SAP agent in each router on that segment copies the information contained in the SAP packet into an internal table called the Server Information table. Because the SAP agent in each router keeps up-to-date information on available servers, a client wanting to locate the gateway server can access a nearby router for the correct internetwork address.
When setting up NetWare, you will need to turn SAP on and enter the number of services you will be advertising to use this feature. See ``Managing NetWare protocols'' for more information.
The NCP makes interaction between clients and file servers possible by defining connection control and service request reply/encoding.
The NCP provides its own session control and packet-level error checking instead of relying on other protocols for these functions. Consequently, the modularity of the protocol stack is reduced, but runs more efficiently.
Each NCP request packet submitted on a given connection must be assigned a sequence number by the client. The first request is assigned the number 1; that number is incremented by 1 for each subsequent request. When a file server finishes processing a request, it places the sequence number for that request in the response packet. The client can then make sure it is receiving the correct responses for the requests submitted.
For more information on IPX, SPXII, RIP, SAP, or NCP, see NetWare transport protocols.