Editing the /etc/asppp.cf Configuration File

The /etc/asppp.cf configuration file provides the PPP link manager on one endpoint machine with information about the machine on the other end of the link--or the machines on the other end of a multipoint (or dynamic point-to-point) link. When the machine boots, the link manager uses this information to establish and maintain communication with a remote endpoint.

Parts of Basic Configuration File

The basic asppp.cf configuration file must contain at least two main sections: an ifconfig line and at least one path section. It can also contain a defaults section, which you use when you want to set the default values for an endpoint. (Refer to Chapter 11, Tailoring Your PPP Link, for a description of keywords used in the defaults section.)

Example 9-1 shows a basic configuration file such as you would create for a remote host to establish a point-to-point link with a dial-in server.

Example 9-1 Basic Configuration File

ifconfig ipdptp0 plumb nomada nubian-ppp up
   path
      interface ipdptp0
      peer_system_name nubian-ppp      # The name in the /etc/uucp/Systems file
      inactivity_timeout 300           # Allow five minutes before timing out

ifconfig Section of the asppp.cf File

The asppp.cf file must contain an ifconfig section with this syntax:

ifconfig interface-number plumb local-machine remote-machine up

Here is a description of the fields:

• ifconfig - Tells the link manager to run the ifconfig command and begin configuring the PPP interface.

• interface-number - Identifies the PPP interface ipdptpn for a point-to-point link or ipdn for a multipoint link. (Replace the n with the number of the interface.)

• plumb - Option of ifconfig that enables IP to recognize the interface.

• local-machine - Gives the name of the local endpoint, which can be the local host name or IP address.

• remote-machine - Gives the name of the remote endpoint, which can be the remote host name or IP address.

• up - Option of ifconfig that marks the interface just described as "up".

The link manager first runs the ifconfig command on the local machine to configure the ipdptp0 point-to-point interface. The zero in ipdptp0 gives the device number of the interface. The plumb option performs various activities necessary for IP to recognize the ipdptp0 interface. nomada is the name of the local host. nubian-ppp is the name of the dial-in server to which nomada connects through the point-to-point link. The ifconfig option up marks the ipdptp0 interface as up.

For more information about ifconfig, see Chapter 10, Troubleshooting PPP, and the ifconfig(1M) man page.

path Section of the asppp.cf File

The path section of the configuration file tells the link manager the name of the remote endpoint and the name of the interface linking the endpoint machines. At a minimum the path section should contain the following lines:

path
   interface interface-number
   peer_system_name endpoint-name

interface Keyword

This keyword defines the PPP interface (either ipdptpn or ipdn). In Example 9-1, the following information appears in the path section:

interface ipdptp0	  
peer_system_name nubian-ppp

The interface keyword identifies ipdptp0 as the point-to-point interface that local endpoint nomada uses to communicate with the remote endpoint in the manner described in this path section. It associates the peer_system_name with the interface.

peer_system_name Keyword

On a dial-out machine such as a remote host, the peer_system_name keyword takes the host name of the remote endpoint as its argument. This is the name of the remote endpoint given in /etc/uucp/Systems. The name need not be the same as the host name on the corresponding ifconfig line.

The argument to the peer_system_name keyword for a dial-in server has a different value. See "Configuration File for Multipoint Dial-in Server" for details.

In Example 9-1, peer_system_name identifies dial-in server nubian-ppp as the remote endpoint at the other end of this link. When the link manager reads the asppp.cf file, it then looks for the entry for nubian-ppp in the /etc/uucp/Systems file. (Recall that the Systems file contains information about how to set up communications with the remote endpoint, including that machine's telephone number. Refer to "Updating /etc/uucp/Systems for PPP".)

inactivity_timeout Keyword

The inactivity_timeout keyword is optional. It tells the link manager that the link can remain inactive for the interval designated. When that interval is passed, the link manager knows to automatically disconnect the link. The default interval is two minutes; you do not have to use inactivity_timeout unless you require a different inactivity interval.

Additional Keywords

You can supply other keywords in the asppp.cf file to define how endpoint machines should communicate. Chapter 11, Tailoring Your PPP Link, has complete information about these keywords.

Configuration File for Multipoint Dial-in Server

The asppp.cf configuration file for a multipoint dial-in server contains the same basic sections as that for a point-to-point link: an ifconfig section, at least one path section, and, if desired, a defaults section.

Example 9-2 shows a configuration file for the dial-in server nubian introduced in Figure 9-1.

Example 9-2 Configuration File for a Multipoint Dial-in Server

ifconfig ipd0 plumb nubian-ppp up

path
   interface ipd0
   peer_system_name tamerlane  # The user name this remote
                               # machine logs in with when it
                               # dials this server
   	peer_ip_address nomada
                               # nomada is a remote machine that
                               # dials in to this server

# nomadb is another remote machine that dials in to nubian

path
   interface ipd0
   peer_system_name lawrence
   peer_ip_address nomadb

# nomadc is another remote machine that dials in to nubian

path
   interface ipd0
   peer_system_name azziz
   peer_ip_address nomadc

ifconfig Section for Multipoint Dial-in Server

The ifconfig section for a multipoint dial-in server has a slightly different syntax than that for a point-to-point link. This syntax is:

ifconfig ipdn plumb server-name up

The major difference is that no destination end points are listed as arguments to ifconfig. Instead, the link manager picks up this information from the path section of the asppp.cf file.

In Example 9-2, the link manager first runs the ifconfig command on the dial-in server to configure multipoint interface ipd0. The zero in ipd0 gives the device number of the interface. The option plumb performs various activities necessary for IP to recognize the ipd0 interface. The ifconfig option up marks interface ipd0 as up.

You may have to supply a netmask + parameter on the ifconfig line if you use subnetting.

path Section for Multipoint Dial-in Server

The path section of the asppp.cf file tells the link manager the name of the remote endpoint and the name of the interface linking the endpoint machines. However, on a multipoint dial-in server, you can include more than one path section. Additionally, some of the arguments to the keywords are used differently with multipoint links.

path
    interface interface-number
    peer_system_name endpoint-username
    peer_ip_address endpoint-hostname

You need to define a path section for each nomadic endpoint with which the dial-in server can establish connections.

interface Keyword

For a multipoint dial-in server, the interface keyword defines the PPP interface ipdn. You must specify the same PPP interface in the path section for every endpoint that communicates with the server through this interface.

peer_system_name Keyword

The peer_system_name keyword takes a slightly different argument for a dial-in machine than a dial-out machine. For a dial-in server, this argument is the login name used by the remote host when it tries to establish communications with the server. This user name must already be present in the server's /etc/passwd file. When the login service reads this name, it verifies the user name in the /etc/passwd and /etc/shadow files enabling communications.

In this excerpt from Example 9-2:

path
    interface ipd0
    peer_system_name scarlett
    peer_ip_address nomadc

the argument to peer_system_name is scarlett, indicating that when nomadc logs in to nubian-ppp, it uses the login name scarlett.

peer_ip_address Keyword

The peer_ip_address keyword is required for multipoint links. It takes the host name or IP address of the remote endpoint as its argument. The example above uses the host name nomads as the argument to keyword peer_ip_address.

Additional Keywords

You can supply other keywords in the asppp.cf file to define how endpoint machines should communicate. Refer to Chapter 11, Tailoring Your PPP Link, for a complete list of keywords.

Editing the Configuration File

When editing asppp.cf:

• Separate keywords in the configuration file by white space (blanks, tabs, and new lines).

• Use a # sign before all character strings meant as comments. All characters placed between a # sign and the next new line are considered comments and ignored.

There are no other format requirements for the placement of the keywords in the file.

How to Edit the asppp.cf Configuration File

1. Become superuser on one endpoint machine and change to the /etc directory.

2. Edit the generic asppp.cf file to add the information defining the PPP link for this machine.

3. Save the file, making sure the permissions are set to 600.

4. Change to the /etc directories on the remaining endpoints and repeat Steps 2 and 3.