Why does my Cisco 3640 not accept the Backup Interface command?

[xzevallos]

I have a 3640 with IOS 12.0(4)T with a Frame Relay serial interface and an ISDN BRI interface. When I enter "backup interface s0/0" under the BRI interface, I get "unrecognized command". When I enter "?" in BRI interface config mode, no backup commands are available. Yet there is no indication in any Cisco documentation that this command is not available with certain hardware, software, or router configuration. Why doesn't my router accept this command?

[tepatel]

BRI interface along with the dialer interfaces are DDR capable interfaces which are always up/up spoofing and never go down..So there is no effect of backup command under that interface..So that command is not available for those interfaces..So no way to use "backup interface xxx" command under the interface which will remain up/up spoofing..

[steve.barlow]

Do you want the serial to be backed up by the bri (i.e. if serial goes down then bri kicks in)?

If yes, then the backup command goes under the serial interface (not the bri).

eg.

interface Serial0/0

backup delay 5 10

backup interface BRI0/0

If no, see Tepatel's message.

Hope that helps

Steve

[xzevallos]

Steve,

That works! My Cisco book made it seem like it works the other way around. Thanks for clarifying this for me.

Xavier