Dynamic VLAN Application Question

[KMoore97150]

I have an VLAN application where I need to find a creative solution.  Suppose you had 4 devices connected to one managed switch and each device was on its own VLAN.  Three of the devices were active on their VLANs and the forth device, on its own VLAN, was a standby or redundant device for any of the others, should a device on VLAN1, 2, or 3 fail.  Can I use dynamic VLANs or programmatically change, on the fly, the VLAN port assignments on the managed switch to connect the device on VLAN4 to the ports that were occupied by the failed device on VLAN1, 2, or 3?  Alternatively, is there another way to accomplish this device swap through switch configuration or programming when the replacement device exists on a different VLAN?  Note that, in this application, due to other constraints, I can't multicast across VLANs without causing issues.

[Francesco Molino]

Hi

Just to be sure to understand your request.
You want the host number 4 to be assigned to the vlan of the failing host from host 1 to 3?
If so, you can configure an eem script that'll be triggered on the interface down status. Let's say host 1 is connected on interface gig1 and vlan 2. If this gig1 goes down, your eem will run and configure host 4 interface to be placed into vlan 2.

Now the question is: what do you want to do if more than 1 host are crashing? Which vlan you want to assign to host 4 interface?

[KMoore97150]

Thanks for your reply.  Yes, you understood my question correctly.  I thought that would be the case for the EEM scripting.  As far as multiple hosts crashing simultaneously, there are multiple use cases that we need to work out.  1) One where all failed hosts are on the same VLAN and 2) One where there are multiple failed devices on multiple VLANs.  We would create a hierarchical evaluation method in our application control software to prioritize the failures.  This should be fairly easy.  We believe, however, somewhat unlikely that devices would simultaneously fail in this manner and we are relatively confident that we can create prioritization method between multiple "standby" hosts.  I am assuming that the EEM scripting is similar but, perhaps, not exactly the same between different CISCO managed switch models.  Is this correct?

[Francesco Molino]

You can use track interface features and group then into track objects with AND aggregator. Then you can create multiple eem based on these track objects. You need to make sure to not overlap otherwise they'll run at the same time and it won't work as expected.
You can also use tclsh scripting or python if you're using an ios-xe device.

[KMoore97150]

Thank you, Francesco. I think that is going to work for us.



Kevin Moore
Director of Research and Development
Bosch Communication Systems
12000 Portland Avenue South
Burnsville, MN 55318
(952) 736-3832 Office
(952) 412- 5387 Mobile


Kevin Moore

Bosch Security Systems

[KMoore97150]

Francesco,



One other question for you.



Do you have any example scripting for Track Interface, Track Objects, and Aggregator functions relating to our VLAN monitoring and switching or can you point us to such examples?



Best Regards,

Kevin Moore
Bosch Security Systems

[Francesco Molino]

Here a link showing how to track an interface status and also use a group object using a list of track with boolean value (and, or).
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/configuration/15-mt/iap-15-mt-book/iap-eot.html#GUID-7D791673-D0FB-4C75-BDAB-30E8AB427862

Once you’ve done this you can run an eem.
Let’s assume your track id is 1 and the interface you to modify is g1/0/4 and assign vlan 20 to it.

event manager applet changeVlanIfce ==> you will have multiple eem which means you can adapt changeVlanIfce by using a name making more sense
event track 1 state down
action a001 cli command "enable"
action a010 cli command "config t"
action a011 cli command "interface g1/0/4"
action a012 cli command "switch access vlan 20"
action z090 cli command "end"
action z999 syslog msg "vlan changed on ifce g1/0/4"