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 NetcomRouter installation uses this standard file to identify the configuration of the devices used to deliver IP traffic over X.25 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. This section does not describe the tunable parameters which affect IP Routing and other items not commonly changed. See Tuning NetcomRouter 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.
The installation script creates one or more WAN/IP devices which are referred to as the xinet interface . Each device named xinetN 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 NetcomRouter devices, the IP address and the file /etc/x25hosts determines 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. Likewise, it it possible to have one ifconfig statement that sets one IP address for several X.25 physical links.
The installation script appends the IP addresses and host names that you provide to the file /etc/hosts. Only the host names are used to create the files /etc/hostname.xinetN, where N is a digit from 0 to 7. During startup, the OS script /etc/rcS.d/S30rootusr examines all files of the form /etc/hostname.driverName[0-9] and creates a TCP/IP stack based on the driver name and IP address defined in the file. If you change IP addresses in the future you only need to edit the file /etc/hosts. However, if you change host names you must edit both /etc/hosts and the appropriate /etc/hostname.xinetN file.
In addition to an IP address and host name, each xinet interface has a network mask. All network mask information is contained in the file /etc/netmasks. The file contains lines with the format:
network_address network mask
Both values are specified in dot notation. If subnets are not being used, then an entry is not required, since the network mask can be determined by network_address.
If the remote hosts are not already part of your /etc/hosts
file, they will be added by the install script. Remote host/X.25
address pairs are used to create the /etc/x25hosts file. 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
NetcomRouter uses to map IP addresses to X.25 addresses. If, in the
future, you wish to add or change entries in the IP address mapping
table, you may edit /etc/x25hosts directly, or you can remove
and re-install NetcomRouter.
The previous section describes the file that configures the TCP/IP protocol stack. This section outlines the file that describes how the protocol stack is to be built. The file describes, for example, that TCP should be linked above IP. And that IP should linked above some Ethernet device and an xinet device. If all you want to do is change the configuration of the stack, the previous section is all you need. If you want to add or delete xinet devices, then you will need to follow this section.
Specifically, /etc/strcf is a file that describes how the protocol stack is built. NetcomRouter uses function x25net in this file to link the xinet device under the IP driver.
For those familiar with TCP/IP traffic in a LAN environment, 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 link00 IP
Here, the IP address remoteIPhost is associated with netid named link00 and a remote X.25 address 12345678. The netid determines the physical wire to be use as described in Changing /etc/packetnets.
Note: The default maximum number of remote X.25 hosts is 20. If your network requires more than 20 entries in /etc/x25hosts, the variable NXINETADDRMAP in the file /etc/conf/pack.d/xinet0/space.c must be changed. See Tuning NetcomRouter
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