Manual TCP/IP Configuration Changes

Introduction

The configuration of the local TCP/IP protocol stack is specified in a file that is read each time you start TCP/IP, including at the time of system boot. The Wanware installation uses this standard file to identify the configuration of the devices used to deliver IP traffic over X.25 or Frame Relay lines.

This section documents the entries in the TCP/IP configuration file, allowing you to modify them, and implement a change to your local IP configuration without reinstalling the product. It also describes how to map a remote IP address to a remote X.25 address or Frame Relay DLCI. This section does not describe the tunable parameters which affect IP Routing and other items not commonly changed. See IP Router Tuning for those details.

Note that the IP addresses in this file may appear as a name (found in /etc/hosts) or as a numeric address. Both are equivalent.

Driver and Device Structure

The installation script creates one or more WAN/IP devices which are referred to as the xinet interface (for IP over X.25) or mpf interface (for IP over Frame Relay). Each device named xinetN or mpfN corresponds to one of eight possible IP network addresses. References to these devices are found in the TCP/IP configuration files.

Often in TCP/IP networks, a local IP address and IP network are assigned to each physical interface. This is done with an ifconfig command. However, with Wanware devices, the IP address and the files /etc/x25hosts and /etc/frelhosts determine the board and link number used to send the data to that host, separate from the interface used. That is, each device represents a logical interfaces -- it is not directly associated with any physical connection. It is therefore possible to have several IP addresses (that is, several ifconfig statements) associated with one physical X.25 link or Frame Relay link. Likewise, it it possible to have one ifconfig statement that sets one IP address for several X.25 or Frame Relay physical links.

TCP/IP Startup Files

The name of the TCP/IP startup file is /etc/rc.d/network.

root uses the startup file to start or stop TCP/IP, as does the operating system when it starts up or changes state. When you add or delete X.25/IP or Frame Relay/IP interfaces (change whether or not a device is to be used), you must change this file.

The startup file reads files in the directory /etc/sysconfig/network-scripts. The files will be named ifcfg-xinetN or ifcfg-mpfN where N is the number of the next device you are using. These files will contain entries of the form:

 
DEVICE=xinetN (or mpfN)
IPADDR=local_ip_address

NETMASK=your_netmask
ONBOOT=yes

IP Address to X.25 Address Mapping

Those familiar with TCP/IP traffic in a LAN environment will know there is a hidden protocol sending information between the systems. Address Resolution Protocol (ARP) maps IP addresses to MAC addresses (for example, Ethernet or Token Ring addresses).

ARP uses broadcasts that send information about the local IP address and the associated local MAC address to everyone on the LAN. Each machine builds a table of IP to MAC address mappings, thereby learning how to contact each IP address. This works well in a LAN environment. However, the necessary broadcast packets that ARP uses do not work well in a WAN environment. You simply cannot broadcast information about your configuration to every system in the X.25 network.

Instead, the installer has to manually build a table that describes the association between each remote IP address and the X.25 address where it can be found. Remote host and X.25 address pairs are stored in /etc/x25hosts. Hosts in this file that are designated to support IP traffic (that is, a host with the IP flag) are added to the addressing mapping table. If, in the future, you wish to add or change entries in the I P address mapping table, you may edit /etc/x25hosts directly. The x25route utility reads this file and passes it to the driver. Whenever you make changes to this file, you will need to rerun x25route.

An entry in x25hosts would look something like this:


12345678 remoteIPhost link0 IP

Here, the IP address remoteIPhost is associated with netid named link0 and a remote X.25 address 12345678. The netid determines the physical wire to be use as described in Changing /etc/packetnets.

Note: The maximum number of remote X.25 hosts is 20.

IP Address to Frame Relay DLCI Mapping

There is also a mapping between remote IP addresses the Frame Relay DLCIs that must be used to reach them. This mapping table is maintained in the file /etc/frelhosts which you may edit directly to add new entries. The froute utility reads this file and passes it to the driver. Whenever you make changes to this file, you will need to rerun froute.

Note: The maximum number of remote Frame Relay hosts is 30.

Revision 6.3.0 (April 2004)