IP SLA Dual Wan Router Backup Settings

I want to discuss about backup redundant dual wan router setting using ip sla. In previous posting, I used bgp as the routing decision maker. Now we are using static route with ip sla. The requirement is to ping loopback0(pretend as server) in R2 from R4-R2.

This is the routing table in R4, default route is pointing to R2

R4#sh ip route
Gateway of last resort is 7.7.24.2 to network 0.0.0.0

     7.0.0.0/24 is subnetted, 2 subnets
C       7.7.24.0 is directly connected, FastEthernet0/1
C       7.7.34.0 is directly connected, FastEthernet0/0
S*   0.0.0.0/0 [10/0] via 7.7.24.2

There are two default route to loopback0 in R2 :

ip route 0.0.0.0 0.0.0.0 7.7.24.2 10 track 1
ip route 0.0.0.0 0.0.0.0 7.7.34.3 100

We use tracking default route to the server in R2

track 1 ip route 0.0.0.0 0.0.0.0 reachability

The tracking is combined with ip sla that use icmp echo to ping server R2 through R4 fa0/1.

R4#sh ip sla statistics

Round Trip Time (RTT) for       Index 1
        Latest RTT: 16 milliseconds
Latest operation start time: *00:38:05.195 UTC Fri Mar 1 2002
Latest operation return code: OK
Number of successes: 346
Number of failures: 20
Operation time to live: Forever

This is the configuration for ip sla in R4 :

ip sla 1
 icmp-echo 2.2.2.2 source-interface FastEthernet0/1
 threshold 3000
 frequency 5
ip sla schedule 1 life forever start-time now

Testing the backup dual wan router :

R4#traceroute 2.2.2.2

Type escape sequence to abort.
Tracing the route to 2.2.2.2

  1 7.7.24.2 24 msec 4 msec *


it is flowing from R4 to R2, then we shut R4 interface fa0/1 so the routing will move through R4 - R3 - R2. The default routing is switched and became like this :

R4#
Gateway of last resort is 7.7.34.3 to network 0.0.0.0

     7.0.0.0/24 is subnetted, 1 subnets
C       7.7.34.0 is directly connected, FastEthernet0/0
S*   0.0.0.0/0 [100/0] via 7.7.34.3

R4#traceroute 2.2.2.2

Type escape sequence to abort.
Tracing the route to 2.2.2.2

  1 7.7.34.3 24 msec 24 msec 4 msec
  2 7.7.23.2 8 msec 12 msec *

Then active interface fa0/1  in R4, so the link between R4 - R2 will become live again :

R4#sh ip route

Gateway of last resort is 7.7.24.2 to network 0.0.0.0

     7.0.0.0/24 is subnetted, 2 subnets
C       7.7.24.0 is directly connected, FastEthernet0/1
C       7.7.34.0 is directly connected, FastEthernet0/0
S*   0.0.0.0/0 [10/0] via 7.7.24.2
R4#

I have attached the gns3 files in this link below, so you can tried it at home.

http://www.4shared.com/rar/xcakXQM8/IPSLA_Backup_Router_Settings.html

Happy labbing