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Cube box-to-box Redundancy

I have two ISR 4451s that are being used as CUBEs.  We are having a problem with box-to-box redundancy.  The two Cubes are using portchannels to provide fail over.    One port of the port channel goes to a 3850 switch (switchA) the other port goes to another 3850 switch (switchB).   We have a layer two link between them.  Each switch has a layer link up to CERs each CER is connected to the ISPs network.  Southbound we are using OSPF to provide connection our network.  The issue is since the CUBEs can pick either switch to send a packet to we have links that are flapping.  Has anybody tried this configuration and gotten to work?  Is so how?

Cisco Employee

Hi James,

Hi James,

As per the following CUBE HA via port channel is not supported

You may check with TAC though if there have been any recent updates regarding the same as this query has been raised with TAC on many cases.




Thank you for your reply.  We

Thank you for your reply.  We are running ISR4451s with 16.3.1 code on them.  The BU has stated that this will work. According to the redundancy options ppt located here  It is supposed to work.  But we are having flapping ports on our switches.


Just wanted to give an update

Just wanted to give an update.  We are trying to use Nexusus 9300s and Vpcs.  We are still having issues.  ARPs are not working correctly.  It appears has if you ping from on the Nexsus to PO2 of the ISR4451,  the ISR4451 does not respond with to the arp resquest from the Nexsus.   We have a TAC case open will let you know what happens.   thanks for you help. 

VIP Advisor

ISR4k and 3850 don't support

ISR4k and 3850 don't support multi-chassis port-channels. This is supported on nexus. You won't be able to aggregate correctly from CUBE to two separate switches. Assuming that I understood the question correctly, you can use backup port feature which will keep one port active at a time and resolve the port flapping which you are facing.


What do you mean backup port

What do you mean backup port feature on the ISR4K.  We are using Redundancy groups.  I am not sure what you mean by backup port feature.

VIP Advisor



Redundancy Groups are used for Box to Box failover.

Now I understood that each CUBE has two uplinks connected to two 3850 switches (one to each switch). Both ports on the CUBE are configured as members of port-channel.

If my understanding is correct, this isn't supported on ISR4k or 3850. This is called vPC (virtual Port Channeling).

You can use 'backup interface' command under interface#1 to point to interface#2 as backup. This means that one interface will be active at a time. The second interface will come online once the primary one fails. This feature will resolve the flapping mac address which you are facing.


CUBE-HA with Port-Channel Config

It has been a few years wince this was last posted. Is Port-channel Configuration supported with CUBE-HA?

VIP Advisor

Have you tried L3 redundancy,

Have you tried L3 redundancy, using HSRP? instead of L2 redundancy

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