Lab 3.3.3: Configuring Callback with PAP authentication

Objectives:

  • Decrease the toll charges of your remote office by enabling callback.

Scenario:

The Atlanta Bread Company is reviewing the costs incurred by the Macon office for dialin access to the core router. A lower telephone rate has been established for your Atlanta office to call to the Macon office. You will configure callback services between the Atlanta core router and the Macon remote office.

Notes: 

Lab Tasks:

  1. Log into the Atlanta router and enter global configuration mode.
  2. Configure the serial interface for callback server mode. The commands to configure the serial interface are:

Atlanta(config)#interface serial 0/1
Atlanta(config-if)#dialer in-band
Atlanta(config-if)#ppp callback accept
Atlanta(config-if)#dialer callback-secure
Atlanta(config-if)#dialer idle-timeout 300
Atlanta(config-if)#dialer wait-for-carrier-time 60
Atlanta(config-if)#dialer hold-queue 50
Atlanta(config-if)#dialer-group 1
Atlanta(config-if)#exit

Below is a brief description of each of the above commands:

dialer in-band Allows us to dial multiple numbers if necessary
ppp callback accept Allows the router to operate as a callback server.
dialer callback-secure Specifies that the router is to disconnect the initial call, and call back only if it has a dialer map command with a defined class for the remote router
dialer idle-timeout 300 Drops connection if there is no traffic for 5 mins.
dialer wait-for-carrier-time 60 Allows up to 1 min. for the connection to occur
dialer hold-queue Holds up to 50 packets while the call is being setup
dialer-group 1 Places this interface in group #1. This is the same as the access-group command for dialers.
Exit Move you out of interface configuration
  1. Create a chat script for your Hayes 56K modem to call the Macon remote office. The command to do this is:

    Atlanta(config)#chat-script hayes56k ABORT ERROR "" "AT Z" OK "ATDT \T" TIMEOUT 60 CONNECT \c
  2. Create a map-class for users that request callback service.

Atlanta(config)#map-class dialer dialback
Atlanta(config-map-class)#dialer callback-server username
Atlanta(config-map-class)#dialer-list 1 protocol ip permit

  1. The final step on the Atlanta router is to map the IP address to the Macon phone number with the "dialback" map class.

    Atlanta(config)#interface serial 0/1
    Atlanta(config)#dialer map ip 10.1.1.2 name macon class dialback modem-script hayes56k broadcast 555600X

  2. Write the configuration to memory.
  3. Log into the Macon router and enter global configuration mode.
  4. Configure the serial interface to request callback services. The command to configure the serial interface is:

Macon(config)#interface serial 0/1
Macon(config-if)#ppp callback request

  1. Write the configuration to memory.
  2. Configure the Macon modem to answer incoming calls by doing a reverse Telnet to the modem. A reverse Telnet is a way to open a terminal session on a modem through the router. It is used to issue commands and save the configuration to the NVRAM of the modem. The following commands can be used to reverse Telnet to the modem on line 2.

Macon#telnet modem2 or "telnet 192.168.0.1 2002"

  1. Enter the "cisco" password at the prompt.

Type "AT" and then press the Enter key. You are now in the modem!
The modem should respond with "OK"
Type "AT&F" and then press the Enter key.
This command will reset the modem to default factory standards.
Type "ATS0=1" and then press the Enter key. This is a "ZERO" not an "O"
This command tells the modem to answer on the first ring.
On the Hayes Accura 56K modem, answer on the first ring, is the only initialization string that we must program on the modem.
Type "AT&W" and then press the Enter key.
This command saves the configuration to the modem's NVRAM

Finally, press Control,Shift, 6 at the same time and then press "X"
This will suspend your reverse Telnet session.
Issue the following command to kill your reverse telnet session on the router:

Macon# disconnect

  1. Turn off both modems. The modems may not get past the LCP negotiation process unless they were powered off and then on. Don't forget to turn the modems back on.
  2. From the Macon router issue the following commands:

Macon#debug dialer events
Macon#ping atlanta

Record your findings about the callback process below:

  1. Save your configurations and turn off all debugging.

Congratulations! You now have callback service on your Atlanta core router and the Macon remote router.