Not everyone knows how powerful the Cisco IP SLA feature is and here an short example what you can do with it.
At first you need to create the monitor in my case I just want to do basic ICMP testings to a specific IP address, you can of course also create other IP SLA operations in the end it just depends for what you need the IP SLA feature.
ip sla monitor 1
type echo protocol ipIcmpEcho 192.168.1.2 source-interface FastEthernet1/0
Then you need to start the IP SLA monitor
ip sla monitor schedule 1 life forever start-time now
With the show command you can look if the tests are successful and then continue with the next step
show ip sla monitor statistics
Here you create the track definition
track 1 rtr 1 reachability
In the end you just need to add the track condition, in my example an static default route
ip route 0.0.0.0 0.0.0.0 192.168.0.2 track 1
When the IP 192.168.1.2 is reachable the static route is within the routing table of the Cisco router, when the IP is unreachable IP SLA deletes the static route from the routing table. I mostly use IP SLA to failover to an back-up internet connection because its very easy to configure.
More information you can find in the Cisco IOS IP SLAs Configuration Guide
That’s maybe not interesting for everybody but when you use Windows Network Load Balancing in your network you should definitively configure static CAM table entries otherwise your VLAN will be flood with multicast traffic. You can create different VLANs for your Windows NLB instances to separate the traffic but that’s more an work around and with static CAM entries nicer from the design.
The static CAM table entries just restrict the multicast traffic to specific ports on your switch where your Servers are located and keep otherwise the network free.
On your router you will have an entry like that:
arp 10.0.0.100 0300.5e11.1111
An static ARP entry with an multicast MAC address
Now to restrict the multicast traffic you use the following command:
mac-address-table static 0300.5e11.1111 vlan 100 interface gi0/10 gi0/11
Which just means that the multicast traffic for VLAN 100 will be flood through the interfaces Gi0/10 and Gi0/11 and all other interfaces will not see the multicast traffic. Its a bit an administrative overhead and you have to think a little bit about that before you can implement but an clean traffic flow within your network.
If you want to read more about it have a look here: Catalyst Switches for Microsoft Network Load Balancing Configuration Example