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Webcast-Catalyst9k
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Using ip unnumbered IPs from DOWN interfaces

I'm building a fairly complex ISDN backup arrangement to backup our frame lines. Ip unnumbered seemed like a great way to simplify the configs. The problem is that I need OSPF, and the PRI serial interface is area 0, and the FastEthernet interface of the client routers are usually not area 0. The frame connections are all area 0, so using ip unnum from the frame interface would work for OSPF, but the whole point is to backup a DOWN frame line. Will I run into problems if the serial interface with the real IP is down but the unnumbered interface is up on a dialer?

Thanks for any guidance with this.

4 REPLIES
Bronze

Re: Using ip unnumbered IPs from DOWN interfaces

Aron,

If the serial interface is down, that interface's address will be unusable by an unnumbered interface. To rectify this, set up a loopback interface in each of your remote routers, and include it in area 0. Have your ISDN interface refer to the loopback interface while running unnumbered. Loopback interfaces never go down.

HTH

Mark

New Member

Re: Using ip unnumbered IPs from DOWN interfaces

Somehow I knew that would be the answer. So I ether have to allocate an IP ahead of time for every router out there that's going to connect with ISDN, or go down the ugly road of trying to move the current WAN segment IP to a loopback in order to start re-using it.

Either that or start assigning addresses to the routers when they connect during ppp negotiation and have those addresses in area 0 on the router and abandon unnumbered.

Hmm..

Bronze

Re: Using ip unnumbered IPs from DOWN interfaces

I don't know the full extent of the network you are planning, but you might be able to use the LAN interface address for the unnumbered interface, and not run OSPF over ISDN. Use floating statics or dialer watch to connect when the frame relay route is lost. This way, you don't need another address for each client, and you don't have to worry about the area assignment.

Mark

New Member

Re: Using ip unnumbered IPs from DOWN interfaces

That won't work here. It's not so much that I need the routes from the backbone injected into the remote routers, they only need access to a few subnets. The problem is that I need to inject static routes into ospf from the remote routers that feed client networks that I don't have any control of.

Floating statics or watches are not an option. These clients are ultra cost-concious and want 100% complete manual control over when the line goes up and down. So I'm making only ICMP traffic to a special address interesting. If they want ISDN, they can type "ping -t 10.1.1.1" and stop the ping when it's time to hang up.

Stupid, yes, but better than talking people through punching keys on an adtran.

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