Let’s talk about ISDN configuration and the related DDR configuration that causes Cisco IOS software to use the BRI interface. You must understand DDR configuration and concepts for the ISDN configuration topics to make sense. ISDN configuration can be very brief. In spite of the noise surrounding all the protocols and terminology, you can configure just a few ISDN options in a router. However, the DDR configuration to tell the router when to dial and when to tear down the call can become quite involved.

The following table summarize the commands used for congiguration:

Command Description Conf. Mode
isdn switch-type switch-type Defines to the router the type of ISDN switch to which the ISDN line is connected at the central office. Global or interface
isdn spid1 spid Defines the first SPID. Interface
isdn spid2 spid Defines the second SPID. Interface
isdn caller phone-number [callback] Defines a valid number for incoming calls when using call screening. Interface
dialer-list dialer-groupprotocol protocol-name{permit | deny | listaccess-list-number |access-group} Defines the types of traffic that are considered interesting. Global
dialer-group n Enables a dialer list on this interface. Interface
dialer string string The dial string used when dialing only one site. Interface
dialer map protocol next-hop-address[name host-name] [spc] [speed 56 | speed 64] [broadcast] [dialstring[:isdn-subaddress]] The dial string to reach the next hop. The map command is used when dialing more than one site. This also is the name used for authentication. The broadcast option ensures that copies of broadcasts go to this next-hop address. Interface
dialer idle-timeoutseconds [inbound | either] Defines how long to wait with no interesting traffic before terminating a dial. Interface
dialer fast-idle seconds If all lines are in use, and new interesting traffic arrives for which another line must be dialed, no dial can occur. fast-idle defines how long to wait to time out the existing dialed lines when this occurs, allowing for a quicker timeout than the normal idle timeout. Interface
controller t1 int-number Selects the channelized T1 interface to be used as a PRI. Global
pri-group timeslotsrange Defines which of the DS0 channels will be used in this PRI. Controller interface subcommand
framing sf | esf Defines the type of framing used on T1-based PRI. Controller interface subcommand
linecode ami | b8zs Defines the type of encoding on T1-based PRI. Controller interface subcommand
show interfaces brinumber [:B channel] Includes a reference to the access lists enabled on the interface. EXEC
show controllers brinumber Shows Layer 1 statistics and status for B and D channels. EXEC
show isdn {active | history | memory | status | timers} Shows various ISDN status information. EXEC
show interfaces brinumber [[:B channel] | [first] [last]] [accounting] Displays interface information about the D channel or the B channel(s). EXEC
show dialer interface brinumber Lists DDR parameters on the BRI interface. Shows whether a number is currently dialed by indicating the current status. Also shows previous attempts to dial and whether they were successful. EXEC
debug isdn q921 Lists ISDN Layer 2 messages. EXEC
debug isdn q931 Lists ISDN Layer 3 messages (call setup/teardown). EXEC
debug dialer {events | packets | map} Lists information when a packet is directed out a dial interface, specifying whether the packet is interesting. EXEC

You can configure DDR in several ways, including Legacy DDR and DDR dialer profiles. The main difference between the two is that Legacy DDR associates dial details with a physical interface, whereas DDR dialer profiles disassociate the dial configuration from a physical interface, allowing a great deal of flexibility. The concepts behind Legacy DDR apply to DDR dialer profiles as well, but Legacy DDR configuration is a little less detailed. Legacy DDR is covered first. DDR can be used to cause the router to dial or to receive a dialed call on asynchronous serial interfaces, synchronous serial interfaces, and ISDN BRI and PRI interfaces. All examples in this chapter use ISDN.

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