TCP/IP Configuration Tips


This section is intended to give some very basic background of TCP/IP terminology and some tips on how to configure TCP/IP on your AS/400 so that you can run the Webulator/400 product. All of the following information refers to TCP/IP for the V3R1M0 version or greater of the OS/400 operating system.

TCP/IP Terms

Internet Network
An internet network is the term used to describe a network that contains a collection of machines communicating together using the internet protocol (IP). The term Internet with a capital "I" is considered THE Internet which is the largest implementation of a network running the internet protocol. All references to an internet network using a lower case "i" refers to a local network which may or may not be connected to the Internet.
Host
The term host is used to describe any machine with an IP address participating on an internet network. This includes workstations and machines running OS/400.
Internet Protocol (IP) Address
A 32 bit number broken up into 4 bytes (each 8 bits in size). The number will be represented as a decimal number with a "." separating each of the 4 bytes. In the decimal notation each of the four numbers can contain a value between 0 and 255. The values 0 and 255 are considered special values (broadcast and loopback) and should not be used when determining a host's IP Address. All machines on an internet network must have a unique IP address. IP addresses include a network and host portion. The network portion is used to determine which network the host resides on, and the host portion is used to uniquely identify the machine within that internet network. This concept can get complicated, especially if subnetting is taking place within your network.
Gateway or Router
A machine that is used to bridge two internet networks together. This is needed when you want to send/receive information outside of your local network. For example, if your AS/400 is going to be connected to the Internet you will need a router to connect your local network to one of the Internet backbone networks (or to a network which is connected through other networks to one of the Internet backbone networks).
Route
A route is used to determine the IP address of a gateway. A route is not needed for information which is being sent to or received from machines which reside on the same internet network.
Subnet Mask
The subnet mask is used to determine what bits of the IP Address are used to assign the network portion. Any bits within the subnet mask that are set to 1 are used to determine the network. You will need additional information beyond this documentation if you intend to set up sub-networks within your internet network. However, we should note that the subnet mask is needed to configure TCP/IP on the AS/400 and further discussion will take place to assist you in setting this value.
Ping
A TCP/IP utility which sends test information and waits for the information to return. The utility displays the amount of data sent and received and the amount of time elapsed while doing so. The utility is very useful when testing the TCP/IP configuration. "Ping" is the name of the command. It accepts one parameter, the IP address or host name of the remote system to send/receive the data.

Assigning your AS/400 an IP Address

If you plan on placing your server on the Internet, you will need to discuss the assignment of the network portion of your IP address with your Internet access provider. If you are not planning on placing your AS/400 on the Internet or your Internet access provider does not currently have a permanent IP address for you, then you are not restricted to the address you want to use. However, as soon as your internet network connects to other internet networks your network's IP addresses must be unique throughout all of the networks connected.

This value can be reconfigured at a later point if you want to the AS/400 to be accessible on the Internet and you don't currently have an Internet access provider or your provider does not have a permanent address that they can assign to you immediately. Note: all hosts on the same network require the same network portion of the IP address and only the host portion of the IP address will be unique per machine.

Assigning the network portion of an IP Address

In the case where the network portion of your IP address has not been assigned to you by a network administrator or an Internet access provider, you can use this section to better understand the network portion and assign one yourself.

The most typical type of network address is a class 'C' address. A class 'C' address begins with the first byte having a value in the range of 192 to 223. For our example we will choose 200 for the first portion of the network address, which indicates that we are assigning a class 'C' address and that we expect to have less than 254 machines on our internet network. For the rest of the network portion we will choose values of 1. Therefore, we will use the address "200.1.1" as the network portion of our IP address.

Assigning the host portion of an IP Address

For our discussion we are assuming that the network portion was defined to be a class 'C' address with no subnetworks defined. With a class 'C' address the last byte will be used for the host portion allowing the address of 1 - 254 to be used for these values. It would make sense for the administrator of this internet network to make all of the host portion assignments and to track these values in order to ensure that each machine is assigned a unique ID.


Working with the OS/400 commands to configure TCP/IP

This section of the Webulator/400 documentation will assist the user in configuring the minimum TCP/IP features necessary to run the Webulator/400 product.

The user must signon as QSECOFR or have equivalent authorities in order to be able to use the following commands effectively. Some of the commands will let you view the information but not change it if you do not have these authorities.

The CFGTCP is an OS/400 command which gives the user a list of options available to configure the TCP/IP interface. Select the Work with TCP/IP interfaces option 1. The user will be presented with a screen that shows the current interfaces configured. An interface as it is presented on this screen refers to the line supporting the TCP/IP protocol and the IP address associated with that line. The *LOOPBACK line is a special line and is required for TCP/IP to operate properly.

To add an interface use option 1 (also available directly as the ADDTCPIFC command). The three required parameters are:

Internet address
The value required for this parameter is the IP address chosen for this AS/400. If the machine is acting as a gateway and has multiple lines being configured to support TCP/IP then this value is the IP address set for the line being configured.
Line description
V3R1 OS/400 TCP/IP does not support all types of line descriptions. Refer to the help information available from this parameter within the ADDTCPIFC command for detailed information about what line descriptions are supported. The typical line descriptions used when configuring a TCP/IP connection for use with the Webulator/400 product would include a permanent connection such as Token Ring or Ethernet LAN connections. This would allow the Webulator/400 product to be available 24 hours a day 7 days a week without incurring additional usage costs. If the Webulator/400 product were to be made available through an Internet connection then either the Token Ring or Ethernet connection could be used along with a router connected to a leased line. The leased line would be permanently connected to the Internet access provider and available 24 hours a day 7 days a week at a fixed rate.
Subnet mask
Set this value to 255.255.255.0 for a class 'C' address which has no subnetworks defined. For any other type of scenarios additional research will be required. Refer to the TCP/IP terms section above for a basic definition of subnet mask.
The other parameters should not require any changes for the basic setup. If you are just getting started or are not connected to any other internet networks then the OS/400 side of things are all up and running ready and are ready to be used.

If you have an Internet connection or a connection with other internet networks, you will need to configure a route to the gateway for data to flow between these internet networks. The CFGTCP command option 2 Work with TCP/IP routes provides a list of already configured routes. Within this option you have the ability to add routes. You will want to add a default route that is used for all traffic that is not destined for the internet network that the AS/400 resides on (machines that contain a different IP Address network portion other than that set for this AS/400 machine). Choose option 1 (also available directly as the ADDTCPRTE command) to add the default route. The three required parameters are:

Route destination
"*DFTROUTE" is the keyword used to indicate the default route.
Subnet mask
"*NONE" is the only valid value to specify for a default route.
Next hop
The IP address of the gateway (router) should be specified for the next hop parameter. This indicates that for the default route all of the information being sent out should next go the gateway machine. From there the gateway machine will use its routing tables to determine where to send the information.

Starting and Testing your TCP/IP Configuration

The STRTCP command is used to start the TCP/IP services on the AS/400. After the TCP/IP services have been configured and started, you will want to test the configuration. The PING command is a good way to test the local and remote TCP/IP configurations.

First use the PING command to test the local configuration by specifying the AS/400's IP address for the Remote system parameter. Check the results of the PING command by looking at the job log. If the job log shows that 100% of the packets sent were received successfully then the configuration on the AS/400 was a success.

After verifying the local configuration the remote configurations can be tested. In order to test any remote configurations you need to have another machine configured and running TCP/IP on your internet network (your gateway is a good test if you have one configured and running). Use the PING command again this time specifying the remote system IP address or host name. Again check to ensure that 100% of the packets were successfully sent and received.

Host Names

Local Host Name Configuration

Up to this point we have discussed the host machines by referencing them using a unique IP address. A second way to reference the host machines is to assign them a host name. A host name is an alternate meaningful name assigned to a host. For example, the host name of www.inetmi.com refers to the web server I/NET is running to demonstrate the Webulator/400 product. The www portion of that name is the host portion the inetmi.com portion is the domain name. The local host and domain name can be set using option 12 (Change local domain and host names). If you are planning on connecting to the Internet you should discuss registering a domain name for your internet network with your Internet access provider.

Problems Starting the Webulator/400 Due to Local Host Name Configuration

The Webulator/400 product requires a local host name to be set either through the TCP/IP configuration, CFGTCP command option 12 (Change local domain and host names) or through the Webulator/400 server host name configuration value. The error message displayed on the STRWBL command indicating this error condition is: "The local host name could not be determined and was not explicitly set."

Remote Host Name Configuration

The CFGTCP command provides multiple ways to assign remote host names. The first way would be to update the local host table using option 10 (Work with TCP/IP host table entries) (this would allow you to map the IP address of the remote machine to a meaningful name). The drawback to doing it this way is that if you have a lot of machines that you would like to reference by name, you have to add them all to this table. A second way of configuring names would be to reference a remote host running the TCP/IP Domain Name Service (DNS) using option 13 (Change remote name server). By using a DNS server hosts can be added to your network with meaningful names without any additional configuration required to remote machines. V3R1 OS/400 TCP/IP does NOT include a the ability to act as a DNS.

Performance Problems Due to Remote Name Server Configuration

Significant performance problems can occur due to an incorrect configuration of the remote name server within the OS/400 TCP/IP. The remote name server, also known as a Domain Name Server (DNS), is used by the Webulator/400 product to query the host name of a machine requesting a document. If this configuration specifies a search first parameter of *REMOTE and the remote DNS does not respond, the server will have to wait for the query to time-out (the number of retry attempts configured also extends the amount of time the request waits before failing). If you do not have a DNS available to you either from your Internet service provider or internally within your organization, you should leave the server address blank and specify *LOCAL for the search first parameter. This should correct your time-out delay, which in turn will increase the speed of the server. The only other side effect to this configuration change is that the access log file will contain the IP address of the machine requesting the document, not the host name.

For additional information concerning the configuration of TCP/IP the user can reference the OS/400 publications or the information provided online by the IBM Corporation.