No announcement yet.

Cisco 2500 ISDN Transparent Backup Bridge

  • Filter
  • Time
  • Show
Clear All
new posts

  • Cisco 2500 ISDN Transparent Backup Bridge


    I'm new to Cisco and I need to configure a transparent backup bridge over ISDN.

    The problem is I only what it to dial when it detects traffic coming from the ethernet from the LAN (serial0). So basically on one end we unplug the ethernet cable to the network until needed. Once manually plugged in it dial's the remote site and in effect forms an uplink cable between switches. We are using two Cisco 4500 routers for this.

    For this do both switches need to be IOS 12? or will 11 suffice.

    Any help would be much appreciated. Really stuck on this one. Thanks

  • #2
    Re: Cisco 2500 ISDN Transparent Backup Bridge

    In order to bridge over ISDN the first step is to ensure the ISDN connects and can pass traffic. After you have that working you can configure the bridging parameters. You need to create the bridge, configure bridging on the LAN interface and to initiate the ISDN you need the following statement

    dialer-list 1 protocol bridge permit

    make sure you configure the isdn with the bridge-goup number as well as the LAN interface. Note if you have other interfaces with bridging enabled this could activate the isdn. If you normally bridge the traffic over a serial interface you could use the backup interface command to prevent the ISDN from activating as long as the WAN interface is up/up. If there is no other bridging and you disconnect the LAN cable then there should be no interesting traffic to initiate the session.

    You will need to do something similar on the other end and if you want either end to be able to initiate it could become a bit tricky in your case. However if the bridge is always initiated in this device you can control the ISDN connectivity as you stated. You can find an example on CCO at the following url