Useful Tips and Tricks This section contains additional notes on some useful methods to properly configure your ISDN network. Although these notes do not apply to all ISDN networks, they address many common configuration mistakes. -
If you want to have only one router to initiate ISDN calls, omit any dialer maps or dial strings on the router that you want to be designated as the called router. The called router will obtain the next -hop and dialer information dynamically. -
For the called router, increase the dialer idle-timeout to a high value. We normally set the dialer idle-timeout value to something such as 9999 so that only the calling router can terminate the call. For example, if you want an ISDN connection to remain up for a minimum of 5 minutes after the call is placed, you must set the dialer idle-timeout value to 300 seconds on the calling router. However, if you do not also adjust the called router's idle timer value, you will see each call terminate after 120 seconds (the default), assuming that no interesting traffic has passed after the connection is made. The called router terminating the connection causes this; so to avoid this, you might want to set the idle timeout value on the called router to an artificially high number. -
Don't forget the broadcast keyword on your dialer map statements. If you are having difficulties getting routes to traverse the ISDN link, odds are good that the broadcast keyword is missing in your dialer map statement. -
If your link appears to stay up indefinitely, or if you see the link constantly connecting right after disconnecting, make your dialer- group list more restrictive . Also, be sure that the ISDN interfaces are listed as passive under your routing processes, -
Be sure to avoid routing loops that might cause the router to consistently dial out. This is especially true when using the OSPF demand circuit feature. This can be accomplished through distribute lists or route maps under the routing processes. -
Keep an open mind. Often, there are multiple ways to accomplish the same goal, and there are a number of ways that any ISDN network can be configured. -
For PPP authentication, be sure that the usernames are configured correctly (remember, they are case-sensitive), and be sure that the passwords match on each router. -
For OSPF demand circuit configuration, be sure to increase the OSPF cost value of the ISDN link so that the preferred path is always over the primary link. Also be sure that there are no routing loops in your network, to avoid calls that are made unnecessarily. -
Configure the optional parameters, such as authentication and caller ID last. Make sure that the ISDN link is working properly first before configuring these advanced options. After each of the steps for configuring ISDN have been completed, use the appropriate show and debug commands to verify that it is working. You should configure the routers incrementally and avoid blindly configuring all the aspects and then trying to figure out where you went wrong. With practice, you will find the method that works best for you, and this will become your default method; however, be prepared to use various methods and understand the " knobs " so that you can address various situations. |
