Here’s an example config for configuring an Cisco ASA5505 with primary and backup ISP’s.
ASA5505(config)# interface ethernet 0/0 ASA5505(config-if)# switchport access vlan 2 ASA5505(config-if)# no shutdown ASA5505(config)# interface ethernet 0/1 ASA5505(config-if)# switchport access vlan 1 ASA5505(config-if)# no shutdown ASA5505(config)# interface ethernet 0/2 ASA5505(config-if)# switchport access vlan 3 ASA5505(config-if)# no shutdown ASA5505(config)# interface vlan 1 ASA5505(config-if)# nameif inside ASA5505(config-if)# security-level 100 ASA5505(config-if)# ip address 192.168.1.1 255.255.255.0 ASA5505(config-if)# no shutdown ASA5505(config)# interface vlan 2 ASA5505(config-if)# nameif primary-isp ASA5505(config-if)# security-level 0 ASA5505(config-if)# ip address 100.100.100.1 255.255.255.0 ASA5505(config-if)# backup interface vlan 3 ASA5505(config-if)# no shutdown ASA5505(config)# interface vlan 3 ASA5505(config-if)# nameif backup-isp ASA5505(config-if)# security-level 1 ASA5505(config-if)# ip address 200.200.200.1 255.255.255.0 ASA5505(config-if)# no shutdown ASA5505(config)# route primary-isp 0.0.0.0 0.0.0.0 100.100.100.2 1 ASA5505(config)# route backup-isp 0.0.0.0 0.0.0.0 200.200.200.2 2