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Beginner

Cisco ACI VPC tunnel up and down flapping every hour

Good afternoon,

We have deployed a Cisco ACI solution with two pods in different DC,s. Recently we have observed from second pod an event related with up-down tunnel flapping. We don´t know if there is some timer in relation with the inactivity of machines attached to EPG. The events only tell as about tunnel up and down with no reason, only show Tunnel configuration incomplete.

Please, somebody has had something similar.

Thank you very much in advanced,

Best Regards,

2 ACCEPTED SOLUTIONS

Accepted Solutions
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Participant

Hey!

The Tunnels you see flapping, are they always towards Leafs residing in the other Pod?

It is normal that ACI Leaf Switches only build a VxLAN Tunnel to Leaf Switches in any other Pod just on-demand.

Meaning if there is traffic going from Leaf 101 in Pod 1 to Leaf 201 in Pod 2, there will be a VxLAN Tunnel established, but if there is no traffic anymore, the Tunnel will be taken down again.

If have seen Tunnel flappings because of this in every Multi-Pod Environment I have accessed so far.

Check if the tunnels you see flapping are also always between Leaf Switches in different Pods.

If yes - this is normal and expected behavior.

Let me know if that helped

Best regards
Julian

View solution in original post

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Hey Daniel,

I am not sure if you can change this behavior, I can check it though.

Checked documentation on Multi-Pod Fabrics real quick.
The whitepapers also just mention that this is expected:
https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739714.html#Buildingdynamictunnels

See section "Building Dynamic Tunnels":

With this information, a dynamic tunnel is created from the Pod2 leaf switch to the Pod1 leaf switch for reverse traffic to use. The reverse traffic will build a complete dynamic tunnel between the two VTEPs or leaf switches. From that point onward, the two endpoints’ communication will be encapsulated leaf to leaf (VTEP to VTEP). The dynamic tunnels, as with normal tunnels in the fabric, are kept alive as long as there is communication between endpoints.

I'll see if I can find some knobs to change that behavior.

Best regards
Julian

View solution in original post

4 REPLIES 4
Highlighted
Participant

Hey!

The Tunnels you see flapping, are they always towards Leafs residing in the other Pod?

It is normal that ACI Leaf Switches only build a VxLAN Tunnel to Leaf Switches in any other Pod just on-demand.

Meaning if there is traffic going from Leaf 101 in Pod 1 to Leaf 201 in Pod 2, there will be a VxLAN Tunnel established, but if there is no traffic anymore, the Tunnel will be taken down again.

If have seen Tunnel flappings because of this in every Multi-Pod Environment I have accessed so far.

Check if the tunnels you see flapping are also always between Leaf Switches in different Pods.

If yes - this is normal and expected behavior.

Let me know if that helped

Best regards
Julian

View solution in original post

Highlighted

Hi Julian,

We are going to check it. But you are right with you approach. We haven´t found any mistake in ACI configuration and talking with other colleages they suspect the same. Do you think changing on-demand behaviour to inmediate could remove it ?

Thank you very much for your fantastic attention,

KR,

 

Highlighted

Hey Daniel,

I am not sure if you can change this behavior, I can check it though.

Checked documentation on Multi-Pod Fabrics real quick.
The whitepapers also just mention that this is expected:
https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739714.html#Buildingdynamictunnels

See section "Building Dynamic Tunnels":

With this information, a dynamic tunnel is created from the Pod2 leaf switch to the Pod1 leaf switch for reverse traffic to use. The reverse traffic will build a complete dynamic tunnel between the two VTEPs or leaf switches. From that point onward, the two endpoints’ communication will be encapsulated leaf to leaf (VTEP to VTEP). The dynamic tunnels, as with normal tunnels in the fabric, are kept alive as long as there is communication between endpoints.

I'll see if I can find some knobs to change that behavior.

Best regards
Julian

View solution in original post

Highlighted

Many Thanks Julian,

It is perfect for us.

Have a nice day !!

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