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With the exception of the host name and
the IP address of the Ethernet interface of each remote site router,
the configuration of each remote site router is the same.
Chat Script Configuration for
Dialing the Central Site
The configuration of each remote router includes the chat-script
global configuration commands shown in Figure .
The chat-script
command defines a chat script named CENTRALDIAL that is used to
place calls to the central site. The CENTRALDIAL chat script
specifies the telephone number (555-1111) of the central site and
the expect-send sequences that guide the modem through the dial-up
process. A key feature of the chat script is that when the remote
router receives the string > (the prompt indicating that the
remote site router has successfully logged in to a central-site
access router), the remote router sends the EXEC command ppp
172.16.2.1. This informs the central-site access router of the
remote router's IP address.
Configuring the Asynchronous
Interface
The configuration of each remote router includes the commands shown
in Figure
that configure the asynchronous interface. The speed
line configuration command
sets the baud rate to 38400 bits per second for both sending and
receiving. The modem-type
command specifies the initialization string sent to the modem when
the interface is reset or when a clear
interface async command is
issued. The initialization string is defined by the modem-def
command for usr-sport-v32. The dialer
rotary-group interface
configuration command assigns asynchronous interface 1 to dialer
rotary group 1.
Using the Site Command
The configuration of each remote router includes the site
configuration commands shown in Figure .
The site global
configuration command defines a remote location that the router can
dial in to or that can dial in to this router, or both, and names it
CENTRAL. The name is used to authenticate the central site when it
dials in.
The dial-on
site configuration command
uses the demand keyword to specify that the central site is
to be dialed and a connection established only when packets are
queued for the central site. The encapsulation
site configuration command
specifies that when the router establishes a connection with the
central site, it is to use PPP encapsulation.
The ip
address interface
configuration command associates IP address 172.16.1.1 with the
CENTRAL site. Note that IP address 172.16.1.1 is the address of the
dialer 20 interface on each of the central-site access routers. The routing
rip interface configuration
command and the broadcast keyword specify that when the
router is connected to the central site, IP routing updates are to
be broadcast, but any incoming IP routing updates are to be ignored.
The dial-group
command specifies that dial group 1 is to be used when connecting to
the central site. Earlier in the configuration, the dialer
rotary-group command assigned
asynchronous interface 1 to group 1.
The session-timeout
site configuration command
specifies that if a period of five minutes elapses during which
there is no input or output traffic, the router is to close the
connection. The system-script
site configuration command
specifies that the CENTRALDIAL chat script is to be used to dial the
central site. The password site configuration command specifies that
when a central-site access router logs in, its password must
be the string "secret."
Static Routing Configuration
The configuration of each remote router includes the ip
route global configuration
commands shown Figure .
The ip route
commands establish static IP routes for networks located at the
central site, all reachable through a next-hop address of
172.16.1.1, which is the IP address shared by all of the access
routers at the central site. All ip
route commands specify an
administrative distance of 1, which is the default.
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