Configuring ISDN Backup for Frame-Relay Subinterface

[ccotech00]

Can anyone pls tell me how to config on a cisco 1721 router the above scenario ,i currently have it configured ,with the BRI interface having it`s own IP address and there is a route with a higher metric than the default route pointing out the bri interface. But for some reason because it is a subinterface the router never sees the interface as down ,even if you drop it ,so it never tries to use the route with the higher metric which in turn never initiates a call on the isdn.

[Richard Burts]

It would help if we knew a few more specifics about your environment and what you have already tried. But here are a few comments that may help.

Floating static routes are a good way to accomplish backup, especially if you are running a dynamic routing protocol over the frame relay subinterface. If you are running a dynamic routing protocol over the subinterface, look in the routing table and find some prefixes that are being learned through that subinterface and note their prefix, mask, and administrative distance. Then create floating statics using the same prefix, same mask, and a higher administrative distance. If you do this traffic will flow over the subinterface as long as the subinteface is up, and traffic will flow over the ISDN if the subinteface stops processing.

Anotheralternative to consider is to configure backup-interface on the subinterface pointing to the ISDN. One consideration here is that the backup will only start when the line protocol of the subinterface goes down.

HTH

Rick

[ccotech00]

Sorry here are some more details : I have a 2620 at the core site with an isdn bri port on it config of bri port : interface BRI1/2

ip address xxxx.xxxx.xxxx.xxxx

encapsulation ppp

dialer-group 1

isdn switch-type basic-net3

no cdp enable

ppp authentication chap

I have a dialer list configured on the router permiting all IP traffic ,and i have also got the username and psw for Chap authentication. The i have a static route to remote network using remote serial ip as next hop and also a floating static route using remote BRI port as next hop.Although the call gets initiated by remote site ,remote site config :

interface BRI0

ip address xx.xx.xx.xx xx.xx.xx.xx

encapsulation ppp

dialer idle-timeout 60

dialer map ip (IP of remote router BRI) name (Name of remote router) (ISDN NO)

dialer load-threshold 90 either

dialer-group 1

isdn switch-type basic-net3

ppp authentication chap

ppp multilink

On this router i also have the floating static configured.This config works on our sites that use point-to-point connections ,but not on this site which is Frame-relay subinterface on 1721.

[sgrenzeb8]

It depends on what IOS you are running, but if you are running a recent one can always use rtr Object Tracking:

Reliable Static Routing Backup Using Object Tracking

http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123newft/123limit/123x/123xe/dbackupx.htm