VRRP and Tracking Network Availability and Performance with IP SLA

By February 14, 2020September 23rd, 2020Blog, Cisco, Networking
networking

Virtual Router Redundancy Protocols can use a function called tracking to follow (track) another portion of the configuration.  Typically when I see this done it’s with the track being done on another interface.  Thus when the “tracked” interface goes down (changes it’s line protocol to down) the track follows that change, and the VRRP configuration attached to it can reduce the priority of a gateway by the decrement amount.

Here is an example of a base VRRP working off an interface tracking:

interface FastEthernet0/0
ip address 10.223.4.2 255.255.255.0
vrrp 1 ip 10.223.4.1
vrrp 1 track 1 decrement 50
!
interface FastEthernet0/1
ip address 172.24.132.5 255.255.255.248
!
track 1 interface FastEthernet0/1 line-protocol

Now that works, but most of the time we don’t care about the interface staying up; we want to ensure that the route downstream is up and working. So we go back to a beloved tool, the IP SLA. IP SLA is a method of active monitoring and reliability reporting. It can be used to generate statistics, or with the track command, modify the router’s behavior based on the statics gathered. We will go over a base example to show how this can be used with VRRP to ensure the best path is used.

So we setup a basic configuration of IP SLA:

ip sla 2
icmp-echo 172.24.132.1 source-ip 1172.24.132.5
threshold 1000
timeout 1000
frequency 1
ip sla schedule 2 life forever start-time now
!
track 2 ip sla 2

This IP SLA checks to see if the IP address 172.24.132.1 is responding with 1 second (1000 milliseconds). If the IP address stops responding within 1 second, the SLA will go from Success to Timeout. The attached track statement will go from Up to Down. If we then attach this to the VRRP statement, we will be able to have the VRRP gateway based on response from its upstream responses, as opposed to the connecting interface being up.

ip sla 2
icmp-echo 172.24.132.1 source-ip 1172.24.132.5
threshold 1000
timeout 1000
frequency 1
ip sla schedule 2 life forever start-time now
!
track 2 ip sla 2
!
interface FastEthernet0/0
ip address 10.223.4.2 255.255.255.0
vrrp 1 ip 10.223.4.1
vrrp 1 track 2 decrement 50
!
interface FastEthernet0/1
ip address 172.24.132.5 255.255.255.248
!

Hope this helps you understand the advantages of using a track statement for IP SLA over just using them to track interface in VRRP.

Jason Howe, PEI

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