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Cisco-based ISDN solution for temporary/backup comms

Posted on 2007-03-29
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Last Modified: 2007-12-19
Hi all,

I'm researching a new solution for providing temporary comms at a remote site. The comms will be ISDN based until the primary comms link is in place. Due to the nature and location of the remote site ISDN calls will be very expensive.

My plan would be to use two Cisco routers with BRI interfaces to achieve the following:

1. Establish “Connectivity Windows” during which users will be aware that comms are up and be able to access remote data, applications, etc.

1a. The remote site will connect automatically at the beginning of a “Connectivity Window” and disconnect automatically at the end of the window.

1b. The line will disconnect automatically if idle for a certain amount of time but will reconnect upon seeing interesting traffic if during a “Connectivity Window”.

2. Calls should only be established from the remote site; however IT users should have the ability to establish a call from our central site if required.

3. If/when the primary comms are in place the ISDN connection should only be used as a backup if the primary comms were to fail.

I’ve used Cisco routers, but using ISDN lines is fairly new to me and certainly the implementation of the above is beyond my current knowledge.

I’m confident in configuring the ISDN interfaces and establishing a connection. What I’m hoping for is some pointers, comments, and feedback on how best to configure the connection to satisfy my requirements.

TIA.


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Question by:rj-smith
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mikebernhardt earned 250 total points
ID: 18819645
1a: ISDN connections require a "dialer list" which defines what traffic is "interesting." In other words, which traffic will bring up and keep up a connection. What you can try it to set up time-based access lists, so that what is interesting can vary with the time of day:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1830/products_feature_guide09186a0080087456.html

1b: You don't need to make the link automatically connect at the right time- ISDN is quick to come up and the first traffic to be interesting will bring up the link. After that, it will stay up or go down as needed, based on your dialer idle-timeout setting. The counter on the idle timeout is reset by packet that match the dialer list.

2: Again, the dialer list can define this.
3. You do this be creating a floating static route to the ISDN dialer interface. As long as the primary link presents a better route, it will use that.
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by:rj-smith
ID: 18841937
Thanks for the information Mike, that sounds pretty promising.

I won't be implementing for a few weeks so I'm not in a position to test or verify the information but I will happily award you the points.

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by:mikebernhardt
ID: 18844311
Your ISDN backup solution is common and easy to implement, and I've done it many times. The more unique part is integrating it with the time-based access list, but ultimately it's just an access list that can be used for any purpose including yours. Let me know how it works!
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