Can I just throw in my two cents here:
I am using IP SLA's in my environment. I have two ISP's to watch in regards to connectivity. DSL interfaces are easy to watch, as the ATM interface is either up or down.
WAN over an interface is a bit trickier, as there are potentially two circumstances that could happen.
1/ The switch/router/interface that your interface is connecting to could die - meaning your connection would be down
2/ The interface on the next hop could go down which would be invisible to you as your interface would still be up yet your connection would be down.
I had to devise a system that would check for these instances are correct the routing table accordingly. I did this through numerous IP SLA's, but a very good feature of the Track objects (which, I don't think is given that much credit) is the boolean operation. You can program a Track object to boolean two other track objects. For instance:
I wanted the Track object 10 (which indicates whether or not my WAN over an ethernet interface is operational) to be noted as down IF either of these two track objects are down:
track 11 interface GigabitEthernet0/2 line-protocol <--- If the actual Interface dies (which encompasses a failing on the next hop)
AND
track 12 ip sla 12 reachability <---- if an ICMP ping operation failed due to a problem 1 hop down the line
delay down 60 up 10
!
In order to track both of these into one Track object I used the boolean operation:
track 10 list boolean and
object 11
object 12
!
This will report the Track object 10, as being down if either one of those circumstances were true. Put a static route into your routing table with the track object of 10:
ip route 0.0.0.0 0.0.0.0 MAIN_ISP 5 track 10
And you're sailing.
I hope this helps.
Tim
Rate if you find helpful.
