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Dial-on-Demand Routing and ISDN Configuration 583
Example 8-27 shows additional configuration on SanFrancisco, in two cases. One shows all IP
packets being considered as interesting, and the other shows all packets to the Web server Lois
(refer to Figure 8-29) considered as interesting.
The dialer-group interface subcommand enables the logic that determines what is interesting.
It refers to a dialer list, which can refer either to an entire protocol suite or to an access list, as
shown. (After the link is up, packets are not filtered using list 101--the logic is used just for
determining what is interesting and what is boring.)
DDR Step 3: Dialing (Signaling)
The dialing router needs additional information before the dial can occur. First, for non-ISDN
interfaces, it is necessary to communicate the dial string to the external dialing device. In-band
signaling (dialing) must be enabled on these interfaces using the command dialer in-band.
This is not necessary on a BRI interface because it uses the out-of-band D channel for signaling.
Table 8-32 summarizes what the command implies on different interfaces.
The second piece of information needed before dialing is the phone number. With the network
in Figure 8-29, the configuration is straightforward. The command is dialer string string,
where string is the phone number. Example 8-28 completes the DDR configuration associated
with Figure 8-29 that allows the dial to occur.
Example 8-27
Defining Interesting Packets to Activate the Circuit from SanFrancisco to LosAngeles
ip route 172.16.3.0 255.255.255.0 172.16.2.1
access-list 101 permit tcp any host 172.16.3.1 eq 80
dialer-list 1 protocol ip permit
dialer-list 2 protocol ip list 101
interface bri 0
encapsulation ppp
ip address 172.16.2.2 255.255.255.0
!Use this one if all IP is considered interesting ...
dialer-group 1
! OR Use next statement to trigger for Web to Server Lois
dialer-group 2
Table 8-32
Effect of the dialer in-band Command
Type of Interface
Type of Signaling Used
Async
AT command set (in-band)
Sync
V.25 bis (in-band)
ISDN
ISDN D channel with Q.921/Q.931 (out-of-band)
ch08.fm Page 583 Monday, March 20, 2000 5:17 PM