Regarding IP SLA

Answered Question
Aug 22nd, 2010
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Hi all,


I want to create redundancy between two ISPs, my design is that I have two routers connected to different ISPs and both are connected to a L2 switch. now i m running HSRP between these routers . I have also implemented SLA on routers. following is the conf for SLA :



ip sla monitor 2
type echo protocol ipIcmpEcho    X.X.X.X
ip sla monitor schedule 2 life forever start-time now

track 2 rtr 2 reachability
delay down 1 up 1


int gi 0/0

standby 10 ip 10.88.0.226
standby 10 timers 5 15
standby 10 priority 110
standby 10 preempt
standby 10 track 2


Now the issue is that I am unable to create redundancy between routers ,even i tried with manually by admin shut down the int. So plz help to sort out the issue.



Thanks

Taran

Correct Answer by kyukim about 6 years 7 months ago

Hi,

Roger pointed out the root cause very well and I want to add one more tip.


I assume you have R1 with hsrp priority 110 and R2 with hsrp priority 100.

When R1's ip sla failed, R1's hsrp priority changed from 110 to 100 as Roger explained.

Now, both R1 and R2 has same hsrp priority 100 and high ip address router becomes a activer router.

If R1's address is higher than R2. (Physical interface IP address), then R1 is still a active router.

You should change R1's hsrp priority to 105, so R1's hsrp priority will be 95 when IP SLA failed and it is lower than R2's 100.


KK.

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ROGER FERNANDO ... Sun, 08/22/2010 - 13:57
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Hi .. i was reviewing your configuration and is all o.k.


Remember that tha active router must have a priority of 110 and the other router (standby) must have 100.


By dafult the system decrement tha priority by 10 if you do not spefied it.


When the reachability fails, the priority is decreases in 10 so the new priority value is 90 which is lower than 100.

Sp the standby router become the active.


use the commands:


sh standby brief, command to check if both routers are negotiationg correctly when you simulate one link is down.


Luck,

Correct Answer
kyukim Sun, 08/22/2010 - 23:02
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  • Cisco Employee,

Hi,

Roger pointed out the root cause very well and I want to add one more tip.


I assume you have R1 with hsrp priority 110 and R2 with hsrp priority 100.

When R1's ip sla failed, R1's hsrp priority changed from 110 to 100 as Roger explained.

Now, both R1 and R2 has same hsrp priority 100 and high ip address router becomes a activer router.

If R1's address is higher than R2. (Physical interface IP address), then R1 is still a active router.

You should change R1's hsrp priority to 105, so R1's hsrp priority will be 95 when IP SLA failed and it is lower than R2's 100.


KK.

tarnhundal Tue, 08/24/2010 - 01:02
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Hi Kim,


Thanks for reply. I got the solution, last time i was doing same but due to decreament of 10 it was not shifting to other router. now i set the priority to 105 and now its working fine .

Kim i have posted one problem and its link is


https://supportforums.cisco.com/thread/2030268?tstart=0



Please help me to sort out the issue because I am unable to sort out this issue till now from a long time.




Thanks

Taran

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