Anyone can help to understand Track ip route 0.0.0.0 0.0.0.0 reachability

Question

Hi All
Please see the diagram in attachment. R7 e1/0 ip address is 7.1.1.7. R3 and R4 are configured with HSRP. R3, R4, R2, and R7 are configured with EIGRP.
HSRP are configured in R3 and R4 as following. Do you think the track configuration is correct ? Thank you
R3(config-if)#do sh run int vlan 4
interface Vlan4
 ip address 4.1.1.3 255.255.255.0
 standby 2 ip 4.1.1.1
 standby 2 preempt
 standby 2 track 1
R3(config-if)#do sh run | s track
track 1 ip route 7.1.1.7 255.255.255.255 reachability
R4(config-if)#do sh run int vlan 4
interface Vlan4
 ip address 4.1.1.4 255.255.255.0
 standby 2 ip 4.1.1.1
 standby 2 priority 105
 standby 2 preempt
 standby 2 track 1
R4(config-if)#do sh run | s track
track 1 ip route 7.1.1.7 255.255.255.255 reachability

Answer 1

As far as tracking goes, it will be "Up" as long as there is a route to 7.1.1.7/32 in the routing table of the routers configured with track 1. It must be a /32 route due to the "255.255.255.255" in the track 1 statement. With that being said, track 1 will be "Down" since e1/0 on r7 is most likely not configured with a /32 mask. I say most likely because it is conneced to R2 and ethernet interfaces cannot be configured with a /32 mask. Attempting to would result in "Bad mask /32 for address 7.1.1.7". To bring track 1 up, the mask needs to match the route for 7.1.1.7 exactly as seen in the routing tables of R3 and R4. 
With the current topology any issue causing eigrp on R2 to not advertise 7.1.1.7/32 will take track 1 down on both R3 and R4. The HSRP priority on both routers will decrement 10 which means that R3 will never take priority. No failover will occur as a permanent state in a converged network.
Another point to make in this scenario is that tracking 7.1.1.7/32 could cause instability in the network. If connectivity between R2 and R7 fails, HSRP will failover. This topology change causes updates and and traffic disruptions in an unrelated part of the network. Traffic destined to R2 or possibly another router off R2 is now affected even though only connectivity to R7 is of concern. Also, R2's hold timer for R7 could cause long delays for eigrp updates to make it down to R3 and R4. 
Optimally, R3 and R4 should track the status of an object specifically related to their own connectivity to R2 such as interface line-protocol or IP. This will give the network stability, increase routing accuracy, cause faster failover, and better avaibility, etc, etc, etc.
Check out Configuring Enhanced Object Tracking @ http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/configuration/15-mt/iap-15-mt-book/iap-eot.html
Ian