Cisco CCNA / CCNP Certification Exam Tutorial: Configuring PPP Callback

You can, in situations where a router needs a remote site to dial into a central router to run, but the budget is much higher when the remote router allows the call. This scenario is perfect for callback when the PPP callback client makes a call to a callback server, authentication is, and then the server depends on the client! This ensures that the client is not paying. The server then calls back to the customer.

InIn the following example, the client was configured and when R2-R1 is the callback server. Lets look at both configurations and requires only the PPP callback commands.

Client:

Forgot your username R1 CCIE

Interface BRI0

IP address 172.12.12.2 255.255.255.0

encapsulation ppp

dialer map ip 172.12.12.1 name R1 5557777 broadcast

Dialer-group 1

isdn switch-type basic-ni

ppp callback

PPP AuthenticationType

Most of this configuration will be familiar to you, but the command PPP callback can not work. This command enables BRI to request a callback.

Pretty simple, right? The PPP callback server configuration requires more configuration and an additional map class as well.

Server:

Forgot your username R2 CCIE
Interface BRI0

IP address 172.12.12.1 255.255.255.0

encapsulation ppp

Dialer callback-secure

dialer map ip 172.12.12.2R2 CALL_R2_BACK class name broadcast 5558888

Dialer-group 1

isdn switch-type basic-ni

accept PPP callback

PPP CHAP

CALL_R2_BACK dialer map-class

User name dialer callback-server

Survey control PPP callback server from top to bottom ...

Dialer callback-Secure provides security for the withdrawal. If the remote router can not be authenticated for the withdrawal, the call is interrupted.

The dialer map statement hoursCALL_R2_BACK calls the class appears at the bottom of the card configuration.

PPP callback can accept PPP callback on this router.

dialer callback-server username callback server says that the statement refers to the device map is a client dialer callback.

The only way to find out if the work configuration and testing, then try to ping from R1 to R2 to see if the withdrawal takes place.

R2 # ping 172.12.12.1

Type cancel the escape sequence.

Sending5, 100-byte ICMP Echos to 172.12.12.1 timeout is 2 seconds:

02:45:42: br0 DDR: Dialing cause ip (s = 172.12.12.2, d = 172.12.12.1)

02:45:42: DDR br0: Attempting to dial 5557777

02:45:42:% LINK-3-UPDOWN: Interface BRI0: 1, was amended in

02:45:42: br0: 1 DDR: Callback negotiated - now separated

02:45:42: br0: DDR 1: Disconnect call

02:45:42:% ISDN-6-CONNECT: Interface BRI0: 1 is now connected to 5557777 R1

02:45:42:% LINK-3-UPDOWN: Interface BRI0: 1,different situation down

02:45:42: DDR: Callback client for R1 created 5,557,777

02:45:42: br0: 1 DDR: disconnecting call .....

Success rate is 0 percent (0 / 5)

R2 #

02:45:57:% LINK-3-UPDOWN: Interface BRI0: 1, changed to

R2 #

02:45:57: br0: 1 DDR: Callback received from R1 5,557,777

02:45:57: DDR: Freeing callback R1 5,557,777

02:45:57: br0: 1 DDR: dialer protocol up

1 02:45:58:% LINE PROTO-5-UPDOWN: Line protocol interface BRI0:been amended

The recall has been successfully negotiated, and then disconnected the call. R1 and R2 then called dialers point to R1, confirmed the end of the call.

R1 # show dialer

type dialer BRI0 - = ISDN

Dial String Successes Failures Last DNIS Last status

5558888 2 4 00:00:20 happened

Zero incoming call (s) have been shown.

0 incoming call (s) rejected for callback.

BRI0 1 - dialer type =ISDN

Idle timer (120 seconds), Fast idle timer (20 sec)

Wait for carrier (30 seconds), resume (15 seconds)

Dialer state of the data link layer up

Dial reason: Callback callback

Time to disconnect 99 secs

Connected to 5558888 (R2)

Pretty cool! Callback is not only important for the transfer of your CCNA and CCNP exams - in a case such as this example shows, the company can save a lot of money!

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