Frame Relay ISDN Backup on Cisco to IBM Router

[donmorales]

Several branches connect to a central site in a Hub and Spoke configuration. The central site has an IBM 2216 with Frame Relay Links, and an IBM 2210 Router with ISDN interfaces. The older branches have IBM 2210 routers that connect to the central site via Frame Relay with ISDN Dial backup. These work fine.

Now we have introduced Cisco 2620 routers in new branches. The Frame Relay links are up and running but we are having difficulty with the ISDN dial backup.

The IBM Routers are configured in such a way that the dialbackup circuit inherit the IP address of the WAN interface when they take over. Can the Cisco 2620 router be configured in a similar manner?

Are there any issues regarding Cisco-IBM interconnectivity on Frame Relay-ISDN dial backup?

[vkapoor5]

If you are using ISDN only as backup, you can try using the 'ip unnumbered ' command on the BRI or dialer interface, where the parameter can refer to the FR interface or sub-interface that you are using. The BRI or dialer interface will then use the IP address of the FR interface. A better option would be to configure the IP address on a loopback interface and then use 'ip unnumbered lo0' on both the FR and ISDN interface.