There are five steps in the configuration of dialer information:
1. Choose the interface.
2. Set the IP address.
Dial-on-Demand Routing (DDR) 845
3. Configure the encapsulation type.
4. Link interesting traffic to the interface.
5. Configure the number or numbers to dial.
Here is an example of how to configure the five steps:
804A#config t
804A(config)#interface bri0
804A(config-if)#ip address 172.16.60.1 255.255.255.0
804A(config-if)#no shutdown
804A(config-if)#encapsulation ppp
804A(config-if)#dialer-group 1
804A(config-if)#dialer string 8358662
Instead of the dialer string command, you can use a dialer map command, which
provides more security:
804A(config-if)#dialer map ip 172.16.60.2 name 804B 8358662
The dialer map command is used to configure the IP address of the next hop router, the
name of the remote router for authentication, and the number to dial to get there. The name is
usually the host name of the remote router, but it must be the name used by the remote router
to identify itself.
Take a look at the following configuration of an 804 router:
804B#show run
Building configuration...
Current configuration:
!
version 12.0
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname 804B
!
ip subnet-zero
!
isdn switch-type basic-ni
!
interface Ethernet0
ip address 172.16.50.10 255.255.255.0
846 Chapter 26 Integrated Services Digital Network (ISDN)
no ip directed-broadcast
!
interface BRI0
ip address 172.16.60.2 255.255.255.0
no ip directed-broadcast
encapsulation ppp
dialer idle-timeout 300
dialer string 8358661
dialer load-threshold 2 either
dialer-group 1
isdn switch-type basic-ni
isdn spid1 0835866201 8358662
isdn spid2 0835866401 8358664
dialer hold-queue 75
ppp multilink
!
ip classless
ip route 172.16.30.0 255.255.255.0 172.16.60.1
ip route 172.16.60.1 255.255.255.255 BRI0
!
dialer-list 1 protocol ip permit
!
The BRI interface is running the PPP encapsulation and has a timeout value of 300 seconds,
which is discussed in the next section. The load-threshold command makes both
BRI channels come up immediately (if you are paying for both, you want them both up all
the time) and is used with multilink, which we will discuss later in this section. The one
thing you should really notice is the number in the dialer-group 1 command. That number
must match the number in the dialer-list command, which is used to define what is
interesting traffic. The dialer hold-queue 75 command tells the router that when it
receives an interesting packet, it should queue up to 75 packets while it is waiting for the
BRI to come up. If more than 75 packets are queued before the link comes up, the packets
beyond the 75 will be dropped.