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:-
=======================
Router#sh run
Building configuration...
Current configuration : 2421 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router
!
boot-start-marker
boot-end-marker
!
enable password XXXXXXX
!
no aaa new-model
dot11 syslog
ip cef
!
!
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
default-router 192.168.1.1
dns-server 218.X.X.X 203.X.X.X
lease 2
!
!
ip name-server 203.124.X.X
ip name-server 218.248.X.X
multilink bundle-name authenticated
vpdn enable
!
vpdn-group 1
request-dialin
protocol pppoe
l2tp tunnel receive-window 1024
!
!
!
!
!
archive
log config
hidekeys
!
!
!
track 1 rtr 1 reachability
!
!
bba-group pppoe global
!
!
interface FastEthernet0/0
description ISP1- Internet Lease Line
ip address 71.X.X.2 255.255.255.0
ip nat outside
duplex auto
speed auto
!
interface FastEthernet0/1
description ISP2- DSL Broadband for Internet
no ip address
ip virtual-reassembly
duplex auto
speed auto
pppoe enable group global
pppoe-client dial-pool-number 1
!
interface FastEthernet0/0/0
description Customer_LAN
ip address 192.168.1.1 255.255.255.0
ip nat inside
ip virtual-reassembly
duplex auto
speed auto
!
interface Dialer1
ip address negotiated
ip mtu 1492
ip nat outside
ip virtual-reassembly
encapsulation ppp
dialer pool 1
dialer-group 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
timeout 1000
threshold 40
frequency 3
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
!
control-plane
!
!
!
line con 0
line aux 0
line vty 0 4
password XXXXXXX
login
!
scheduler allocate 20000 1000
end
Router#
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.
http://www.cisco.com/wwl/export/crypto/tool/stqrg.html
export@cisco.com.
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)