Let me document some basic TCP/IP stuffs for OS/2 Warp 4.5 in the form of FAQ as a memo to myself. I seem to forget these easily as OS/2 is not my primary operating system. The information contained in this page is purely based on my experience and I don't guarantee correctness and/or completeness.

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Q. What is the simplest way to configure TCP/IP?
A. Open TCP/IP Configuration Notebook from WPS or by executing tcpcfg2 from the command line.

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Q. Can I configure it from the command-line?
A. Yes, OS/2 provides common networking utilities like ifconfig. See examples below.

Command	Description
ifconfig lan0	Show the current configuration of the first LAN interface
netstat -r	Show the routing table
arp -a	Print the arp table
tracerte www.google.com	Print route packets on the way to www.google.com
iptrace lan0	Capture packets transmitted over lan0 into iptrace.dmp
ipformat -f iptrace.dmp	Print iptrace.dmp in a human-readable format

You can find more networking utilities in C:\MPTN\BIN. You can get help on them by executing tcphelp.

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Q. What file initializes a NIC with an IP address upon start-up?
A. C:\MPTN\BIN\SETUP.CMD. The TCP/IP Configuration Notebook can overwrite this file as necessary.

The file shows the following contents when I enable DHCP on the first LAN interface.


When I switches to a static IP address of 192.168.2.21 with the default gateway of 192.168.2.1, it shows the following.

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Q. How can I change my host name?
A. You can set the host name by setting HOSTNAME in config.sys.


Alternatively, you can open TCP/IP Configuration Notebook and enter the host name in the Host Names tab as shown below.


Note:

• The host name is different from the NetBIOS computer name you can set in C:\IBMLAN\IBMLAN.INI.
• The host name doesn't map to an IP address of your computer automatically. You may need to create an entry in %ETC%\HOSTS.

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You may use TCP/IP Configuration Notebook to change the contents of this file instead of modifying it directory.

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Q. Where can I find the simple host name lookup information like /etc/hosts in *nix?
A. %ETC%\HOSTS


You may use TCP/IP Configuration Notebook to manipulate the host names in this file.

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Q. How can I make a TCP/IP program resolve a host name via the host file before having contacted a domain name server?

A. You can change the default behavior of contacting a domain name server by setting the environment variable USE_HOSTS_FIRST. Setting this environment variable regardless of its value makes a properly written TCP/IP program resolve a host name via the host file first, then try a domain name server.

Let's assume the following sample host file.

[C:\]set USE_HOSTS_FIRST=

[C:\]set USE_HOSTS_FIRST
USE_HOSTS_FIRST=(null)

Pinging to www.yahoo.com sends ICMP packets to the IP address resolved via a domain name server.

The behavior changes after having set USE_HOSTS_FIRST. The ping program sends ICMP packets to 192.168.1.3 instead.

You can add the environment variable to CONFIG.SYS to make the new behavior permanent.


If you don't like to change config.sys manually, you can open TCP/IP Configuration Notebook and check Look through Hosts list before going to Name Server.