I am posting an article for circuit redundancy used in working scenario.
Router is Cisco 1841 with IOS image c1841-spservicesk9-mz.124-15.T12.bin.
Router has three Fast Ethernet interfaces, each one for ISP1, ISP2 and customer LAN.
Router is connected with two Internet circuits.
Primary as internet lease line (ILL) with static IP connected to ISP1.
Backup as PPPOE broadband with dynamic IP address connected to ISP2.
You can configure both circuits to work in Primary/backup mode using Cisco SLA monitor services and static route.
Below is the Router's config:-
Current configuration : 2421 bytes
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
enable password XXXXXXX
no aaa new-model
no ip dhcp use vrf connected
ip dhcp excluded-address 192.168.1.X
ip dhcp pool Customer_LAN
network 192.168.1.0 255.255.255.0
dns-server 218.X.X.X 203.X.X.X
ip name-server 203.124.X.X
ip name-server 218.248.X.X
multilink bundle-name authenticated
l2tp tunnel receive-window 1024
track 1 rtr 1 reachability
bba-group pppoe global
description ISP1- Internet Lease Line
ip address 71.X.X.2 255.255.255.0
ip nat outside
description ISP2- DSL Broadband for Internet
no ip address
pppoe enable group global
pppoe-client dial-pool-number 1
ip address 192.168.1.1 255.255.255.0
ip nat inside
ip address negotiated
ip mtu 1492
ip nat outside
dialer pool 1
no cdp enable
ppp authentication chap callin
ppp chap hostname XXXXXXX (Hostname/Username given by ISP)
ppp chap password 0 XXXXX (Password given by ISP)
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 71.X.X.1 track 1
ip route 0.0.0.0 0.0.0.0 Dialer1 200
ip http server
no ip http secure-server
ip nat inside source route-map ISP1-NAT interface FastEthernet0/0 overload
ip nat inside source route-map ISP2-NAT interface Dialer1 overload
ip sla 1
icmp-echo 71.X.X.1 source-interface FastEthernet0/0
ip sla schedule 1 life forever start-time now
access-list 1 permit 192.168.1.0 0.0.0.255
no cdp run
route-map ISP1-NAT permit 10
match ip address 1
set interface FastEthernet0/0
route-map ISP2-NAT permit 10
match ip address 1
match interface Dialer1
line con 0
line aux 0
line vty 0 4
scheduler allocate 20000 1000
Cisco IOS Software, 1841 Software (C1841-SPSERVICESK9-M), Version 12.4(15)T12, RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2010 by Cisco Systems, Inc.
Compiled Fri 22-Jan-10 00:40 by prod_rel_team
System returned to ROM by reload at 11:24:31 UTC Mon Oct 11 2010
System image file is "flash:c1841-spservicesk9-mz.124-15.T12.bin"
This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.
Processor board ID FHKXXXXXXXX
3 FastEthernet interfaces
DRAM configuration is 64 bits wide with parity disabled.
191K bytes of NVRAM.
62720K bytes of ATA CompactFlash (Read/Write)