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Flexlink Support on Catalyst 9000 Series

May I know whether Cisco Catalyst 9000 Series switches supported Flexlink? I have checked all configuration guide included IOS 16.6 document for Catalyst 9300, but cannot find. Thank!



Cisco Employee

Flexlinks has been deprecated on Cat9K on 16.x release train.



Is this just for Cat9k? For example, I see that "switchport backup interface" in the 16.3.x config guide for 3850s. However, I just installed 16.8.1a on a test 3850, and noticed there is not a command for a backup interface. Is it being deprecated for all release on all platforms?


Software Configuration Guide, Cisco IOS XE Denali 16.3.x (Catalyst 3850 Switches) - Configuring Wireless High Availabi…



Flex links has been deprecated for all Switching platforms on the 16.x release.

The feature still works on older 3.6/3.7 releases for switching.

Thank you,



Can we possibly influence this obviously very poor decision? Flexlinks is still very useful and sometimes the only possible way to deal with diverse scenarios. I have a situation with Cisco IE switches for example, they are running a ring topology and the only "way out" from this environment is Flexlinks.



We understand this is a helpful feature in your deployment.

Do you have an SE that you work with?  If yes, please reach out to me via that channel.  If no, please have TAC reach out to Enterprise Switching Product Management team and we will look at the request.

Thank you.


Thanks Jagbir! I will prepare some more info on one of the cases and go via TAC or via my local SE. Sort of difficult to drive such case as it's right in between support and design. Thx.


hello jaqbir,

we also asked the same dev since 6 months

we had a case on that and we engaged the sales team

we got an answer from product dev that flexlinks will no be longer supported

as essen said that is a very bad decision

3.6 is now finished and end of support

we have no continuity in the release branch


What's the alternative? 


I would also second this, dropping support for flex links is a very short sighted move by Cisco.


In industrial configurations its often the only simple method of achieving redundancy when coupling devices using an MRP ring into an STP structure elsewhere in the network without resorting to having L3 routing between the areas.


I have a configuration right now trying to connect another vendors industrial kit using MRP into a 3850 stack and I simply cannot achieve it at L2 without flex links. The other vendors kit has a similar system to flex link but not as effective and it doesn't support port-channels so it's no good.


Do Cisco have some alternative options? Perhaps you can consider introducing MRP outside of the IE range if flex links are no longer supported?



An alternative would to be use ip sla and EEM scripting to monitor a primary interface and if that fails enable the backup interface




.ip sla 10
 icmp-echo x.x.x.x source-IP  x.x.x.x
 timeout 200
 frequency 5
ip sla schedule 10 life forever start-time now

track 1 rtr 10 reachability


        or without ip sla

track 1interface FastEthernet0/0 line-protocol

event manager applet FA00-UP
event track 1 state up
action 5.0 cli command "enable"
action 5.1 cli command "conf t"
action 5.2 cli command "interface FastEthernet0/1"
action 5.3 cli command "shut"
action 5.4 cli command "end"

event manager applet FA00-Down

event track 1 state down
action 5.5 cli command "enable"
action 5.6 cli command "conf t"
action 5.7 cli command "interface FastEthernet0/1"
action 5.8 cli command "no shut"
action 5.9 cli command "end"


kind regards

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

This is an interesting answer and there are obvious use cases for EEM in this fashion so thank you for the input.


Howver, I think it would be a tad complex to achieve dynamic link management without operator intervention at some point using EEM in the same way flex links operated though. It could definitely operate as an last resort backup but the admin would need to then go and manually swap the system back to the normal interfaces after investigation.


Effectively one needs to achieve a link swap in the event of loss of throughput no matter which of the pair is currently active.

We cannot rely solely on link down as a port misconfig could prevent config even if the link is up, so the IP SLA example gives us a good option here.


But effectively what we would need to achieve is. Whichever interface is currently active, if we lose ICMP then shut that interface and open the other.


Achieving this with EEM seems like it would be a challenge, we also would not be able to achieve preemptive fallback in any way I can immediately think of, because we are shutting the "failed" interface we then cannot monitor to establish if connectivity is recovered.


Flex links seems as if it offered a solution to all of these issues.



Cisco Employee





And planned for C3K ?


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