The asppp.cf configuration file for a dynamic-link configuration must contain information about remote hosts and the interfaces to use for the PPP link. After the dial-in server boots, its link manager uses this information to establish communications whenever the server is called by a remote endpoint.
The asppp.cf configuration file for a remote host is the same as the one described in "Parts of Basic Configuration File", except for the addition of the parameter negotiate_address:
ifconfig ipdptp0 plumb dummy mojave up path interface ipdptp0 peer_system_name mojave-ppp connectivity_timeout 300 negotiate_address on |
The negotiate_address parameter indicates whether local IP address assignment is obtained through negotiation and assigned dynamically. If set to "on", the IP address supplied by the server is used as the client's local address for the duration of the connection.
When the dial-in server receives an incoming packet, the link manager reads the path sections of its configuration file to identify the remote endpoint and determine the interface to use. The configuration file shown in Example 24-4 does not contain an interface keyword. Instead, the link manager uses interface information established in the defaults section.
The asppp.cf configuration file for a dial-in server with dynamically allocated links might look like the following:
ifconfig ipdptp0 plumb mojave clienta down ifconfig ipdptp1 plumb mojave clientb down ifconfig ipdptp2 plumb mojave clientc down # This means grab whatever interface is available (not in use) defaults interface ipdptp* # Each path specifies a machine that might dial up / log # in to this server path peer_system_name tamerlane # nomada uses the login name # tamerlane path peer_system_name lawrence # nomadb uses the name lawrence # for login path peer_system_name nomadc |
The ifconfig section for a dial-in server with a dynamically allocated link has the syntax:
ifconfig ipdptpn plumb server-name client-address down
Example 24-4 contains three ifconfig lines, each initializing a point-to-point interface.
ifconfig ipdptp0 plumb mojave clienta down ifconfig ipdptp1 plumb mojave clientb down ifconfig ipdptp2 plumb mojave clientc down |
When you configure a dynamically allocated link, you might want to include a defaults section in the asppp.cf file. This section sets the defaults for the value replacing keyword, wherever keyword subsequently appears in the asppp.cf file. The syntax for the defaults section is:
default keyword |
Example 24-4 uses the keyword interface to define the interface as ipdptp*, indicating a dynamic link. The asterisk wildcard tells the link manager to use any available ipdptp interface defined in the ifconfig section. Thus the link manager on server mojave uses either ipdptp0, ipdptp1, or ipdptp2--whichever is the first interface configured "down" that it finds.
The configuration file for the server with dynamic links must contain path sections for every remote host permitted to establish connections with the server. The path section has the following syntax:
path peer_system_name endpoint-username |
No interface keyword has been defined in the path section because this value is defined in the defaults section. The peer_system_name keyword has the same meaning here as it does in the configuration file for the multipoint server. See "path Section for Multipoint Dial-in Server" for more information.
You can supply other keywords in the asppp.cf file to define how endpoint machines should communicate, including the use of security keywords as explained in "Configuration Keywords".