[c-nsp] A few very Quick IP SLA questions

[Drew Weaver]

Hi all, happy Friday.

A few questions regarding configuring IP SLA.

I've configured two IP SLA probes as such:

ip sla 1
 icmp-echo x.x.25.97 source-ip x.x.25.98
 frequency 10
ip sla schedule 1 life forever start-time now

ip sla 2
 icmp-echo x.x.25.101 source-ip x.x.25.102
 frequency 10
ip sla schedule 2 life forever start-time now

1) If I want this probe to run forever, is it best to configure it as a recurring probe or have the lifetime be 'forever'?
2) If the router has multiple paths to the destination does specifying the source-address mean that 100% of the time it will use the Interface that the indicated source address is assigned to?
3) When using the 'track command' (for example: track 100 ip sla 1 reachability | state) What is the functional difference between reachability and state? Wouldn't they be the same thing?

Also the main reason for implementing this is because we had an instance where a interface didn't go down, but no traffic would pass through it (routing protocols failed, etc) and we have our default routes setup as such:

ip route 0.0.0.0 0.0.0.0 Vlan4091 x.x.25.97
ip route 0.0.0.0 0.0.0.0 Vlan4092 x.x.25.101

So return traffic was still being sent down the 'dead but up/up' interface which caused obvious heartache.

Would using a track on each of these routes (combined with aforementioned IP SLA probes) be a good way to prevent this from occurring in the future?

I basically want to ensure that both the interface is up and that traffic can pass from this router to its gateway before the route will be used.

Sorry this is so long, hopefully it makes at least some sense.

I thought about using BFD, but it seems like they have removed support for BFD on VLANs in recent code.

Thanks,
-Drew