Troubleshooting network communications

User's Guide
PART 4. Database Administration and Advanced Use
CHAPTER 26. Client/Server Communications

Troubleshooting network communications

Network software involves several different components, increasing the likelihood of problems. Although we provide some tips concerning network troubleshooting here, the primary source of assistance in network troubleshooting should be the documentation and technical support for your network communications software, as provided by your network communications software vendor.

Ensure that you are using compatible protocols

If you have more than one protocol stack installed on the client or server computer, you should ensure that the client and the database server are using the same protocol. The -x command line switch for the server selects a list of protocols for the server to use, and the CommLinks connection parameter does the same for the client application.

You can use these options to ensure that each application is using the same protocol.

By default, both the database server and client library use all available protocol stacks. The server supports client requests on any active protocol, and the client searches for a server on all active protocols.

For more information about the -x switch, see The database server. For information about the CommLinks connection parameter, see CommLinks connection parameter.

Ensure that you have current drivers

Old network adapter drivers are a common source of communication problems. You should ensure that you have the latest version of the NDIS or ODI driver for your network adapter, as appropriate. You should be able to obtain current network adapter drivers from the manufacturer or supplier of the card.

Network adapter manufacturers and suppliers make the latest versions of drivers for their cards available. Most card manufacturers have a Web site from which you can download the latest versions of NDIS and ODI drivers.

You may also be able to obtain a current network adapter driver from the provider of your networking software.

When you download Novell client software, it has ODI drivers for some network adapters in addition to the Novell software that is used for all network adapters.

Switch off your computer between attempts

Some network adapter boards do not reset cleanly when you reboot the computer. When you are troubleshooting, it is better to turn the computer off, wait a few seconds, and then turn it back on between attempts.

Diagnose your protocol stack layer by layer

If you are having problems getting your client application to communicate with a database server, you need to ensure that the client and the database server are using compatible protocol stacks.

A helpful method of isolating network communication problems is to work up the protocol stack, testing whether each level of communication is working properly.

Verify that the data link layer is working

If you can connect to the server computer in any way, then the data link layer is working, regardless of whether the connection is made using the same higher-layer protocols you will be using for Adaptive Server Anywhere.

For example, you may want to try to connect to a disk drive on the computer running the database server from the computer running the client application.

Having verified that the data link layer is working, the next step is to verify that other applications using the same network and transport layers as Adaptive Server Anywhere are working properly.

Testing a NetBIOS protocol stack

If you are using Windows for Workgroups, Windows 95, or Windows NT, and you are using the native protocol, try using the chat or WinPopup application. This tests whether applications on the client and server computers can communicate with each other.

If you are running NetBIOS network communications software under OS/2, you should confirm that you can establish a connection between the computers running the client application and the database server using one of the applications that come with your network software.

You should ensure that the applications that come with your networking software are running properly before testing Adaptive Server Anywhere.

Testing a TCP/IP protocol stack

If you are running under TCP/IP, there are several applications that you can use to test the compatibility of the client computer and server computer TCP/IP protocol stack. The ping utility provided with many TCP/IP packages is useful for testing the IP network layer.

Using ping to test the IP layer

Each IP layer has an associated address—a four-integer period-separated number (such as 191.72.109.12). Ping takes as an argument an IP-address and attempts to send a single packet to the named IP-protocol stack.

First, determine if your own protocol stack is operating correctly by "pinging" yourself. If your IP-address is 191.72.109.12, you would enter:

ping 191.72.109.12

at the command line prompt and wait to see if the packets are routed at all. If they are, the output will appear similar to the following:

c:> ping 191.72.109.12
Pinging 191.72.109.12 with 32 bytes of data:
Reply from 191.72.109.12: bytes=32 time<.10ms TTL=32
Reply from 191.72.109.12: bytes=32 time<.10ms TTL=32
Reply from 191.72.109.12: bytes=32 time<.10ms TTL=32
...

If this works, it means that the computer is able to route packets to itself. This is reasonable assurance that the IP layer is set up correctly. You could also ask someone else running TCP/IP for their IP address and try pinging them.

You should ensure that you can ping the computer running the database server from the client computer before proceeding.

Using telnet to test the TCP/IP stack

To further test the TCP/IP stack you can start a server application on one computer, and a client program on the other computer, and test whether they can communicate properly.

There are several applications commonly provided with TCP/IP implementations that can be used for this purpose: here we show how to use telnet to test the TCP/IP stack.

Start a telnet server process (or daemon) on one machine. Check with your TCP/IP software for how to do this. For a typical command line telnet program you would type the following instruction at the command prompt:
```
telnetd
```
Start the telnet client process on the other machine, and see if you get a connection. Again, check with your TCP/IP software for how to do this. For command line programs, you would typically type the following instruction:
```
telnet server_name
```
where server_name is the name or IP address of the computer running the telnet server process.

If a telnet connection is established between these two machines, the protocol stack is stable and the client and server should be able to communicate using the TCP/IP link between the two computers. If a telnet connection cannot be established, there is a problem. You should ensure that your TCP/IP protocol stack is working correctly before proceeding.

Diagnosing wiring problems

Faulty network wiring or connectors can cause problems that are difficult to track down. Try recreating problems on a similar machine with the same configuration. If a problem occurs on only one machine, it may be a wiring problem or a hardware problem.

For information on detecting wiring problems under NetWare, see your Novell NetWare manuals. The Novell LANalyzer program is useful for tracking down wiring problems with Ethernet or TokenRing networks. Your NetWare authorized reseller can also supply you with the name of a Certified NetWare Engineer who can help diagnose and solve wiring problems.

A checklist of common problems

For Info For a description of network communication parameters, see Network communications parameters.

The following list presents some common problems and their solutions.

If you receive the message Unable to start — server not found when trying to start the client, the client cannot find the database server on the network. Check for the following problems:

The network configuration parameters of your network driver on the client machine are different from those on the server machine. For example, two Ethernet adapter cards should be using a common frame type. For Novell NetWare, the frame type is set in the net.cfg file. Under Windows 95, OS/2, and Windows NT the settings can be accessed through the Control Panel Network Settings. In Windows for Workgroups, it can be accessed through Network Settings in the Windows Setup.
Under the TCP/IP protocol, clients search for database servers by broadcasting a request. Such broadcasts will typically not pass through gateways, so any database server on a machine in another (sub)network, will not be found. If this is the case, supply the host name of the machine on which the server is running using the -x command-line option.
Your network drivers are not installed properly or the network wiring is not installed properly.
The network configuration parameters of your network driver are not compatible with Adaptive Server Anywhere multi-user support. See Configuring your network adapter board for a description of configuration parameters that affect performance and may affect operation of the client and server.
If your network communications are being carried out using TCP/IP, and you are operating under Windows for Workgroups or Windows NT, check that your TCP/IP software conforms to the Winsock 1.1 standard.
If you receive the message Unable to initialize any communication links, no link can be established. The probable cause is that your network drivers have not been installed. The server and the client try to start communication links using all available protocols unless you have specified otherwise using the -x option. Check your network documentation to find out how to install the driver you wish to use.