This sample configuration dynamically routes IP between two IOS routers using the RIP routing protocol and PPP with CHAP authentication over ISDN. With RIP as the routing protocol, routing updates are constantly exchanged between the two routers. The periodic exchange of routing updates requires the ISDN line to be permanently active regardless of traffic demands. This is known as a nailed-up connection.

Though some cases might require a nailed up ISDN connection, most applications do not. Permanently active ISDN lines can result in potentially high ISDN costs and this configuration should only be used if ISDN billing is not a concern. Otherwise, it is highly recommended that a dial-on-demand routing (DDR) configuration is used. A DDR configuration activates the ISDN line only when there is traffic to send. DDR can be implemented either with a snapshot routing protocol to resolve routes dynamically or with static routes.

Get A DDR Configuration Using Snapshot Routing (recommended)
Faxback Doc #0511

Get A DDR Configuration Using Static Routes
Faxback Doc #0511

Info On PPP Faxback Doc #ppp

Info On Snapshot Routing Faxback Doc #snapshot

Info On IP Unnumbered Faxback Doc #ip_unnum

Before You Begin

Get The IOS ISDN Command Glossary. Faxback Doc #0551 Detailed descriptions of all IOS commands used in ISDN configurations. Also provides links to the IOS Command Reference if more information is required

Get The IOS Command Line Interface Tutorial Faxback Doc #ios_tutorial Instructions on configuring an IOS router using the command line interface

Note: Commands followed by a <*> are on by default and do not have to be configured. The "!" marks that appear in the configuration are automatically entered by the router and function as line separators for easier reading.

Atlanta Router Configuration
In IOS "show running-config" format

version 11.2 <*>
service udp-small-servers <*>
service tcp-small-servers <*>
!
hostname Atlanta
!
enable secret cisco
!
username Boston password gocisco1
ip subnet-zero
no ip domain-lookup
isdn switch-type basic-ni1
!
interface Ethernet0
 ip address 10.1.1.1 255.0.0.0
!
interface BRI0
 no ip address <*>
 encapsulation ppp
 dialer rotary-group 0
 isdn spid1 014045551111000 5551111
 isdn spid2 014045552222000 5552222
 no fair-queue <*>
 no cdp enable <*>
!
interface Dialer0
 ip unnumbered Ethernet0
 encapsulation ppp
 dialer in-band
 dialer idle-timeout 300
 dialer map ip 20.1.1.1 name Boston speed 56 broadcast 16175553333
 dialer map ip 20.1.1.1 name Boston speed 56 broadcast 16175554444
 dialer hold-queue 10
 dialer load-threshold 200 either
 dialer-group 1
 no fair-queue <*>
 no cdp enable <*>
 ppp authentication chap
 ppp multilink
!
router rip
 version 2
 network 10.0.0.0
 no auto-summary
!
ip classless
ip http server
!
dialer-list 1 protocol ip permit
!
line con 0
 password console
 login
line aux 0 <*>
line vty 0 4
 password telnet
 login
<*>
!
end <*>

Boston Router Configuration
In IOS "show running-config" format

version 11.2 <*>
service udp-small-servers <*>
service tcp-small-servers <*>
!
hostname Boston
!
enable secret cisco
!
username Atlanta password gocisco1
ip subnet-zero
no ip domain-lookup
isdn switch-type basic-5ess
!
interface Ethernet0
 ip address 20.1.1.1 255.0.0.0
!
interface BRI0
 no ip address <*>
 encapsulation ppp
 dialer rotary-group 0
 isdn spid1 0155533330 5553333
 isdn spid2 0155533330 5554444
 no fair-queue <*>
 no cdp enable <*>
!
interface Dialer0
 ip unnumbered Ethernet0
 encapsulation ppp
 dialer in-band
 dialer idle-timeout 300
 dialer map ip 10.1.1.1 name Atlanta speed 56 broadcast 14045551111
 dialer map ip 10.1.1.1 name Atlanta speed 56 broadcast 14045552222
 dialer hold-queue 10
 dialer load-threshold 200 either
 dialer-group 1
 no fair-queue <*>
 no cdp enable <*>
 ppp authentication chap
 ppp multilink
!
router rip
 version 2
 network 20.0.0.0
 no auto-summary
!
ip classless
ip http server
!
dialer-list 1 protocol ip permit
!
line con 0
 password console
 login
line aux 0 <*>
line vty 0 4
 password telnet
 login
<*>
!
end <*>

After You've Tried

You've tried the configuration and it doesn't work. Help is available!

Get IOS Router ISDN Troubleshooting Assistance Faxback Doc #isdn_ts

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