Backup interface

[a.elsherif]

Actually i have a 2600 router which is equipped with one serial port, one ISDN port, i need to add a third (sync/async port or analogue modem port )that will be used as a backup for the previous two ports . Can something like this be implemented. Please Advice

[cymurai]

If you have a 2600 with a WIC-2T or WIC-2a/s serial modual then you have 2 serial ports, the other serial port can be config to either sync or async/analog backup, take your pick.

If you NEED to you can even use CON or AUX ports(not recommended).

[thisisshanky]

As recommended by the other post, the hardware configuration can be setup.

Once that is done, you can use floating static routes, with different admin distances, to achieve failover.

[vcjones]

Providing backup for an ISDN link is a little trickier than just adding another floating static route. Dial-on-demand links are never down from the viewpoint of the router, so the analog backup route will never float into use. You can do the job using dialer watch and an easily filtered routing protocol such as RIPv2 or EIGRP. See the white paper on my web site for an explanation of how it works (the white paper was written before dialer watch and uses BGP to implement equivalent functionality). For more details, see the dial backup chapters in my book High Availability Networking with Cisco.

Good luck and have fun!

Vincent C Jones

[a.elsherif]

Dear Sir

actually ineed to keep the ISDN port as a backup interface to the serial port. This can be done quite easy with the (backup interface type no.).

But what is not easy for me is when installing a sync/async port, how to let this port to be backup for the previous two ports . that is when the serial is down the isdn is up and when the serial is up the isdn is down . when the serial is down and the isdn didnot go up, the async port should be activated , and when the serial is up the async port goes down once again.

[vcjones]

I assumed in my original answer that you already had ISDN backup of your leased line working using dialer watch or dial on demand routing. If you read the references, you will find that you need to use a routing protocol with filtered advertisements to detect when the primary link is up (so no backup is needed), when the backup link is up (so the async backup is not needed), and when neither preferred link is up (so the async backup is needed).

Another consideration is whether or not you want ISDN to keep trying once async comes up. If not, there is a trick you can use which does not require dialer watch or fancy routing.

Good luck and have fun!

Vincent C Jones