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ISDN backup - ip vs. unnumbered and interesting traffic choices

We have 4 PRIs and remote sites with BRIs for backup of our Frame Relay network. PRIs are in a 7204 and BRI WICs are in 2600s usually. We are using ACS on the 7204s with TACACS+ authentication.

I want to set things up so my cusomers can control the ISDN coming up in a very controlled way. For example just tell my remote sites to start a special "ping -t" to bring up/keep up the line. Reason for this is most of my clients are extremely cost concious and don't want automated use resulting in long distance ISDN charges.

Most of the remote sites are redistributing static subnets into OSPF so a floating route to the wrong place is BAD unless I do some "distribute list outs" on the ospf config.

The other issue is IP addressing... I'm tempted to do ip unnumbered for these connections even though the frame WAN uses 30bit subnets for management.

Any problems with this approach? Thoughts?

Thanks, ajs


Re: ISDN backup - ip vs. unnumbered and interesting traffic choi

I prefer IP unnumbered for dial links, particularly for dial backup. That way, I can use a single, simple configuration on each spoke router that can dial any available hub router and not worry about which hub router the spoke happens to connect to! The details (and several caveats) are in chapter 7 of my book "High Availability Networking with Cisco." See the listings on my web site for some example configurations. Just make sure the "target" IP is not the highest numeric value loopback on the router or you may confuse routing protocols such as EIGRP and OSPF which require a unique router identifier.

Good luck and have fun!

Vincent C Jones

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