The Cisco-proprietary version of HDLC is the default encapsulation type for serial and ISDN interfaces.

R2#show interface serial0

Serial0 is up, line protocol is up

  Hardware is HD64570

  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255

  Encapsulation HDLC, loopback not set, keepalive set (10 sec)


While there’s only one D-channel in BRI, PRI (US) and PRI (EU), the bandwidth of that D-channel does vary from BRI to PRI.  It’s 16 kbps in BRI and 64 kbps in both PRI versions.

The global command isdn switch-type must be configured before you can even begin to have ISDN work.  show isdn status will tell you whether or not you’ve done this correctly.

R2#show isdn status

 **** No Global ISDN Switchtype currently defined ****

ISDN BRI0 interface

        dsl 0, interface ISDN Switchtype = none

    Layer 1 Status:

        DEACTIVATED

    Layer 2 Status:

        Layer 2 NOT Activated

    Layer 3 Status:

        0 Active Layer 3 Call(s)

PAP allows passwords to be different; CHAP requires that they be the same.

PAP requires the “ppp pap sent-username” interface-level command.  CHAP has no equivalent command.

Define interesting traffic with dialer-list and link that list to the interface with dialer-group.

R2#conf t

R2(config)#dialer-list 1 proto ip permit

R2(config)#int bri0

R2(config-if)#dialer-group 1

The dialer idle-timeout value is expressed in seconds, not minutes.  (Even IOS Help isn’t totally clear on this.)

R2(config)#int bri0

R2(config-if)#dialer-group 1

R2(config-if)#dialer idle-timeout ?

  <1-2147483>  Idle timeout before disconnecting a call

R2(config-if)#dialer idle-timeout 120


Dialer map maps a remote IP address to a remote phone number.  You never dial the local router’s phone number.

dialer load-threshold requires the ppp multilink command to be configured, and the value of dialer load-threshold is expressed as a ratio of 255, NOT 100.  For example, if you want the second b-channel to come up when the first reaches 50% of capacity, the value to express with dialer load-threshold would be 50% of 255 – which equals 127.

R2(config)#int bri0

R2(config-if)#encap ppp

R2(config-if)#ppp multilink

R2(config-if)#dialer load-threshold ?

  <1-255>  Load threshold to place another call