Aux Port Unnumbered IP Dial-on-Demand Routing

The following is a sample configuration for IP Unnumbered Dial-on-Demand Routing (DDR) using the auxiliary port. The two routers will exchange routing informat ion using RIP. Only IP unicast traffic will bring the call up. RIP broadcasts will not initiate a call and will not keep the line active.

Sample Configuration For Answering Router ------------------------------------------------------- Current configuration: ! version 10.2 ! hostname Snoopy ! enable password test ! username Woodstock password peanuts ! interface Ethernet0 ip address 172.16.10.1 255.255.255.0 ! interface Serial0 no ip address shutdown ! interface Serial1 no ip address shutdown ! interface Async1 ip unnumbered Ethernet0 encapsulation ppp async default ip address 172.16.20.1 async dynamic routing async mode dedicated dialer in-band dialer idle-timeout 300 dialer map ip 172.16.20.1 name Woodstock broadcast ppp authentication chap dialer-group 1 ! router rip network 172.16.0.0 ! access-list 100 deny ip 0.0.0.0 255.255.255.255 255.255.255.255 0.0.0.0 access-list 100 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255 ! dialer-list 1 list 100 ! ip route 0.0.0.0 0.0.0.0 172.16.20.1 ip route 172.16.20.1 255.255.255.255 async1 ! line con 0 line aux 0 modem ri-is-cd speed 38400 flowcontrol hardware line vty 0 4 password cisco ! end !

Explanation of Snoopy configuration

Current configuration:
!
version 11.0
!
hostname Snoopy

Snoopy is the name of this router. This name will be passed by this router in a ppp authentication process. It is case-sensitive. The opposite router, Woods tock, must have a username Snoopy defined (see below for username description).

!
enable password test
!
username Woodstock password peanuts

The username "Woodstock" is the hostname of the opposite router and is reference d in the dialer map command for authentication purposes. The username is case sensitive and must match the opposite router's hostname exactly.

The password peanuts is used as the ppp authentication password for the user Woodstock. It is case sensitive and must be the same as the password for username Snoopy on the Woodstock router.

Note: To avoid confusion, the unencrypted form of the password peanuts is shown in this sample configuration. In the actual configuration, the password would appear in its encrypted form: (i.e. 7 13061E010803 where 7 denotes the encrypti on type and 13061E010803 is the encrypted form of the password peanuts.) When entering or making changes to the username command, always type the password in its unencrypted form. Do not enter the encryption type (7). It is set automatic ally.

interface Ethernet0 ip address 172.16.10.1 255.255.255.0 ! interface Serial0 no ip address ! interface Serial1 no ip address ! interface Async1 ip unnumbered Ethernet0 encapsulation ppp async default ip address 172.16.20.1

This command assigns the address 172.16.20.1 to the opposite router's Async interface. It is necessary because we are using unnumbered interfaces between the two routers. 172.16.20.1 is the IP address of the opposite router's etherne t 0 interface. This address is used because the previous command "ip unnumbered Ethernet0" points the Async interface to the local Ethernet 0 IP address.

async dynamic routing

This command allows routing protocols to be run over the async interface to resolve IP routes dynamically. If the command is omitted, static routes can still be used.

async mode dedicated

This command enables the configured session type to start automatically when the DDR link comes up. In this example, PPP encapsulation is defined.A PPP session will be automatically be used by the router for this interface. Note that with this command, an interactive login is not possible.

dialer in-band

The dialer in-band command specifies that DDR is to be supported on the interface.

dialer idle-timeout 300

This command sets the number of seconds the connection will remain open if no interesting traffic is being routed across this link. The timer is reset each time an interesting packet is forwarded across the DDR connection. The idle-timeout should be set to the same value on both routers. In this example, the line will drop after 5 consecutive minutes without interesting traffic.

dialer map ip 172.16.20.1 name Woodstock broadcast

With this command, the name "Woodstock" will be used to authenticate the dial in user. If authentication is successful, the ip address 172.16.20.1 will be mapped to the remote user. Note there is no telephone number specified, as this site will not be calling the other.

The following describes the parameters of the dialer map command in more detail:

172.16.20.1 is the IP address of the opposite router's Async interface. Since we are using IP unnumbered interfaces, this will be the same as the IP address assigned to Ethernet 0 on the opposite router.

name Woodstock is the hostname of the opposite router.The name is case sensitive broadcast enables broadcast packets to be forwarded to this address. (i.e. IP RIP or IGRP updates).

!
ppp authentication chap
dialer-group 1

The dialer-group 1 command associates this interface with the dialer-list 1 definition. The interface will now consider anything defined in dialer-list 1 as interesting traffic.

router rip
network 172.16.0.0
!
access-list 100 deny ip 0.0.0.0 255.255.255.255 255.255.255.255 0.0.0.0
access-list 100 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255

The access list is used to create a filter. In this example, the packets that the access list will permit will be referenced by the dialer-list command to determine interesting packets.

The following explains the access-list parameters in more detail:
The number 100 is the list identifier. All access-list commands with the same identifier define a single filter. Ordering of the access-list commands is very important. An statements in an access-list are stepped through one by one until a match is found. Once a match is found, any access-list definitions that follow are ignored. Although not displayed, there is always an implicit deny all statement at the end of an access-list. Therefore, if a packet reaches the end of an access-list without matching a permit statement,it will be automatically blocked.

access-list 100 deny ip 0.0.0.0 255.255.255.255 255.255.255.255 0.0.0.0 will determine all broadcast packets to be uninteresting. Specifically, RIP updates will not initiate a call nor reset the dialer idle-timeout counter. access-list 100 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255 will determine all other IP packets to be interesting.

dialer-list 1 list 100 This command references the filter defined by access-list 100. Packets permitted by access-list 100 will be considered interesting packets for a DDR interface be longing to dialer-group 1.

ip route 0.0.0.0 0.0.0.0 172.16.20.1

This command creates a static default route. This is required because routes resolved dynamically are lost when the link is down. If the router receives a packet that is destined to a network not listed in its routing table, the router will forward this packet to 172.16.20.1. In this case, this is the address of the opposite router.

ip route 172.16.20.1 255.255.255.255 async1

Since the Async interface is unnumbered, a second static route is needed to tell the local router which interface to use to get to 172.16.20.1. A mask of 255.255.255.255 is used to specify this route as a host address.

! line con 0 line aux 0 modem ri-is-cd

This command allows the router to only accept incoming calls. Reverse telnet to the modem is not possible when this command is used. To reverse telnet, you must change this to modem InOut. After reverse telnet is completed, you can change this back to modem ri-is-cd.

speed 38400

38400 is the maximum speed for the auxiliary port.

flowcontrol hardware
line vty 0 4
!
end

Sample Configuration for Dialing Router: ----------------------------------------- Current configuration: ! version 10.2 ! hostname Woodstock ! enable password test ! username Snoopy password peanuts chat-script dialnum "" "atdt\T" TIMEOUT 60 CONNECT \c chat-script rstusr "" "at&fs0=1e0&r2&d2&c1&b1&h1&m0&k0" "OK" ! interface Ethernet0 ip address 172.16.20.1 255.255.255.0 ! interface Serial0 no ip address ! interface Serial1 no ip address ! interface Async1 ip unnumbered Ethernet0 encapsulation ppp async default ip address 172.16.10.1 async dynamic routing async mode dedicated dialer in-band dialer idle-timeout 300 dialer map ip 172.16.10.1 name Snoopy modem-script dialnum broadcast 14085554321 dialer-group 1 ppp authentication chap pulse-time 3 router rip network 172.16.0.0 ip route 172.16.10.0 255.255.255.0 172.16.10.1 ip route 172.16.10.1 255.255.255.255 async1 ! access-list 100 deny ip 0.0.0.0 255.255.255.255 255.255.255.255 0.0.0.0 access-list 100 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255 ! dialer-list 1 list 100 ! line con 0 line aux 0 modem InOut speed 38400 script reset rstusr flowcontrol hardware line vty 0 4 password test login ! end

Explanation of Woodstock Configuration

Current configuration:
!
version 10.2
!
hostname Woodstock
!
enable password test
!
username Snoopy password peanuts

Note that this router, Woodstock, has a username defined for the opposite router Snoopy, and Snoopy has a username defined for Woodstock. Both these username statements use the same password peanuts.

!
chat-script dialnum "" "atdt\T" TIMEOUT 60 CONNECT \c

A chat script can be used to send commands to the modem. CHAT scripts are case sensitive. This script is named dialnum and when called upon, sends the atdt string to the modem. The \T causes the script to send the phone number that appears in the dialer map statement.

chat-script rstusr "" "at&fs0=1e0&r2&d2&c1&b1&h1&m0&k0" "OK"

When rstusr is called upon, the modem string, at&fs0=1e0&r2&d2&c1&b1&h1&m0&k0 will be sent. This string is the appropriate modem configuration setting for a USRobotics Sportster Modem. Other modems will require similar settings, but different syntax. In this example this script is executed by the command, script reset rstusr that follows. The reset string will insure that the modem is always set with the same settings.

!
interface Ethernet0
ip address 172.16.20.1 255.255.255.0
!
interface Serial0
no ip address
!
interface Serial1
no ip address
!
interface Async1
ip unnumbered Ethernet0
encapsulation ppp
async default ip address 172.16.10.1
async dynamic routing
async mode dedicated
dialer in-band
dialer idle-timeout 300

Note, the dialer idle-timeout value is the same as on the Snoopy router.

dialer map ip 172.16.10.1 name Snoopy modem-script dialnum broadcast 14085554321

This dialer map command is similar to that used on the Snoopy router. The command essentially maps a name for authentication, modem script to use, and phone number to reach a certain destination IP address. The following describes the parameters of the dialer map command in more detail:

172.16.10.1 is the IP address of Snoopy's Async interface. Since we are using IP unnumbered interfaces, this will be the same as the IP address assigned to Ethernet 0 on Snoopy.

name Snoopy is the hostname of the opposite router. The name is case sensitive and should also be defined in the username statement above.

Modem-script dialnum specifies that the chat-script dialnum should be sent on dial out.

broadcast enables broadcast packets to be forwarded to this address. (i.e. ip RIP or IGRP updates and ipx RIP and SAP updates).

14085554321 is Snoopy's telephone number. This is the number we need to dial to get to the other site.

dialer-group 1 ppp authentication chap pulse-time 3

This enables pulsing DTR signal intervals on the interface to ensure that the modem properly disconnects. This is needed on the dialing router only.

router rip
network 172.16.0.0

ip route 172.16.10.0 255.255.255.0 172.16.10.1
ip route 172.16.10.1 255.255.255.255 async1
!
access-list 100 deny ip 0.0.0.0 255.255.255.255 255.255.255.255 0.0.0.0
access-list 100 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255
dialer-list 1 list 100
!
line con 0
line aux 0
modem InOut

The modem InOut command allows the auxiliary port to make outgoing and answer incoming calls.

speed 38400

The maximum speed for the auxiliary port is 38400.

script reset rstusr

This command sends the chat-script rstusr whenever the line resets.After a call drops, the line will reset and the rstusr initial configuration string will be sent to the modem insuring that the modem will be properly configured to accept the next incoming call.

flowcontrol hardware
line vty 0 4
password test
login
!
end

Posted: Tue Nov 26 11:27:10 PST 1996