Actual use-case for IP SLA Tracking to affect routing?

[vv0bbLeS]

Hello all,

We can of course use IP SLA's and Track objects to track reachability of a next-hop (like an ISP) and then remove a route to affect our routing, but I'm trying to think of an actual use-case where I would actually do this, as opposed to just letting my routing protocol (e.g. BGP, EIGRP, OSPF) handle the failover for me (by simply assigning a worse metric to my alternate route) ?

[paul driver]

Hello
various use cases which could be:
*static/dyanmic route advertisement based on a certain condition or boolean AND/OR oprerations:
route(s) being present/or not 
link status
path reachability

*polilcy based routing < dual routing path and you wish to policy route specific routes to both of them and still have resiliency

*Failover - FHRP (hsrp -glbp-vrrp)

*EEM scripting pertaining to a certain action to be performed on the rtr- shutdown/enable a link -  flush a nat table - add a route - enable a feature etc,,, 

[julian.bendix]

Had a customer once with lots of very small branches.. each of those having one landline and a LTE backup.

Customer had old and small Cisco Routers out there not set for any replacement or hardware refresh, and the LTE backup was on a metered contract.

Best solution which I could come up with was tracking the reachability over the landline with an IP SLA.. having a default route with a tracker through said landline.
Another default route through the LTE backup with AD 200 which only gets active once the IP SLA through the landline fails.

My preferred solution here would be Meraki or something but I had to work with what was already there.
Hope this helps.

BR Jules

[Joseph W. Doherty · Accepted solution]

The "classical" usage case is using tracking with static routing.  As you note, if using dynamic routing, tracking isn't as useful except for OER/PfR.  For the latter, that technology could optionally use IP SLA to determine best path.

Personal real world example: one of our MPLS providers has a node that became a black hole, but routing continued to have that as the good path.  OER/PfR's IP SLA detected the issue and dynamically injected routing updates to not use a "valid" path that could not get to destination.

[Giuseppe Larosa]

Hello @vv0bbLeS ,

>> as opposed to just letting my routing protocol (e.g. BGP, EIGRP, OSPF) handle the failover for me (by simply assigning a worse metric to my alternate route) ?

There are cases where you are connecting two different companies that don't want to share a dynamic routing protocol for policy reasons.

For this kind of cases the use of static routes + IP SLA + tracking is preferred over simple static routing.

Specially if there is a LAN switch or any other way that can make an interface up even if the remote device is down.

Hope to help

Giuseppe

[vv0bbLeS]

Excellent, thank you all!