Motorola 2200 - Manual (Page 239)

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set ip backup-gateway option [ on | off ]
Turns the backup gateway option on or off. Default is off.
set ip backup-gateway interface [ ip-address | ppp-vcc n ]
Specifies the backup gateway inter face ip address to which you want to direct the backup connection.
set ip backup-gateway default ip_address
Specifies the ip address of the default gateway.