Incorrectly Configured IP Address on Dialer interface

Incorrectly Configured IP Address on Dialer interface

 

In many cases, engineers might select to statically configure the static IP address, purchased from the ISP, directly on the dialer interface. If all settings are correct and the ISP has provided the correct IP address you should expect no surprises.

 

It happens many times though, that the incorrect IP address has been provided and when the router authenticates to the ISP it is unable to route any packets towards the Internet.

 

The short and effective way around this problem is to never assign any IP address to the Dialer interface unless it's required. Services such as Crypto VPN tunnels to remote offices, various Internet services served to the Public (mail, web etc.) do not usually require you to configure the statically assigned IP address directly to the Dialer interface.

 

Allowing the ISP take care of the IP address assignment to your Dialer interface will in many cases help you avoid these problems completely.

 

For the purpose of our example, assuming we've got an incorrect IP address configured, following is the repeated behaviour we would encounter:

 

• R1# debug ppp negotiation

PPP protocol negotiation debugging is on

 

*Apr 26 00:26:53.815: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access3, changed state to up

*Apr 26 00:26:54.525: Di0 IPCP: Install route to 80.106.108.2

*Apr 26 00:26:54.529: Di0 IPCP: Remove route to 80.106.108.2

*Apr 26 00:26:54.529: Di0 IPCP: Remove default route thru 80.106.108.2

*Apr 26 00:27:34.624: Di0 IPCP: Install route to 80.106.108.2

*Apr 26 00:27:34.629: Di0 IPCP: Remove route to 80.106.108.2

*Apr 26 00:27:34.629: Di0 IPCP: Remove default route thru 80.106.108.2

*Apr 26 00:28:00.579: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access3, changed state to down

 

The router will continuously install and remove the default route provided by the ISP. The Virtual-Access interface is then shutdown and brought back up. This behavior will continue non-stop until you either shutdown the Dialer interface or correct the problem.

 

Changing our tactic, we decide to correct this problem and let the Dialer interface negotiate the IP address from our ISP:

 

• R1# config terminal
• Enter configuration commands, one per line. End with CNTL/Z.
• R1(config)# interface dialer 0
• R1(config-if)# ip address negotiated
• R1(config-if)# end
• R1#

 

On the next cycle of negotiation, the Dialer interface is assigned its IP address:

 

*Apr 26 00:34:48.667: %LINK-3-UPDOWN: Interface Virtual-Access3, changed state to up

*Apr 26 00:34:48.667: %DIALER-6-BIND: Interface Vi3 bound to profile Di0

*Apr 26 00:34:50.655: %LINK-3-UPDOWN: Interface Dialer0, changed state to up

*Apr 26 00:34:52.595: Di0 IPCP: Install negotiated IP interface address 94.70.33.251

*Apr 26 00:34:52.599: Di0 IPCP: Install route to 80.106.108.2

*Apr 26 00:34:53.217: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access3, changed state to up