IP SLA implementation

_Gonzalo_

We have recently had problems at work with HSRP and IP SLAs. We connect through redundant links that are not controlled by us, and one of them has been dropping some packets intermittently. This caused HSRP active gateway to go standby, and after a short time it would recover again.

There is a single IP SLA configured, and when the network dropped these packets it was the only responsible of bringing the active HSRP switch down.

I was wondering if it would not be best to have two IP SLAs with increased timers synched, so small packet losses would not be that much of an issue.

An example:

One SLA that pings every 10 seconds and decreases 20 to priority
Two SLAs that ping every 10 seconds and decrease priority by 10. One would start 5 seconds after the other.

The only bad thing about it would be having another process running on the router, but I don´t think that having a process that sends a ping can be that costly...

So... Does it make sense? Have you seen it done somewhere?

Thanks in advance!

(I edited the timers)

sandman748

if its just a small amount of packet loss (less than three minutes) you can delay the object going down on the track statement

sample config

track x sla y
delay down 90


if you wanted to have a second sla to another site in case the object you are tracking is flaky you can also track a boolean list so that both sites have to stop responding to ping for the hsrp to fail over

example

track 1 ip sla 1
track 2 ip sla 2
track 3 list boolean or
object 1
object 2

We use a combination of both for our dual ISP wan connection. So on track 3 we also have

delay down 90 up 180

The end result is that both responders have to be down for 90 seconds before the HSRP state change and back up again for 3 minutes before it changes back.

Obviously those timers can be tweaked to your liking. It doesn't have to be that long before going down or back up.