Vlan issues: Multiple subnets with the same vlan id on the same switch

[john.stanford]

Here is the situation that a customer of ours has:

Background:

When the original data center was constructed the customer created seperate networks with L3 to the Core Router.  Since different teams manged each network, vlan assignments were never monitored.  As a result, the company used vlans 100 through 110 on 3 different networks with different subnets on each network connected thru SVI's on different switches.  The switches are EOL/EOS and need replacement, also the "pizza box servers"(1 & 2U servers) and Blade servers are now EOL/EOS. Our plan is to migrate to a vPC pair of Nexus 9396's and migrate all the VM's from the Blade servers to a new Flexpod environment using UCS FI 6332-16G's and NetApp AFF series SAN.

Here is the issue:

With the elimination of the old switches where the SVI vlan gateways are located, the gateways need to be migrated to the new Nexus 9396's   This is causing the issue, How to support these 3 subnets on the same vlan ID?

Here are some of the ideas the team has thought of:

VXLAN: Creating a new design document with numbering standards ie:  10000 - 19999 Management, 20000 - 29999 VM Management, 30000-39999 DMZ, 40000-49999 Accounting, etc.  Also, I believe the migration to ACI (planned for the future, hence the N9K's) will be easier.  The only problem I see is that if we have to propagate the vlan northbound to other switches we will have to convert back to physical vlans.

Renumbering the offending vlans: This method will obviously work, however the new vlans will not follow any standard for vlan numbering.

Subinterfaces:  Don't like this method, Old Technology.  The CTO suggested this method, I have to prove this is not the best method.

Looking for any other options....

Thank you,

John

[Dennis Mink]

you could support 3 subnets on a single interface by using secondary IP addresses, it is possible.

so that could answer your question

his is causing the issue, How to support these 3 subnets on the same vlan ID?

I am unsure on how these direct connected networks could/will be propagated through dynamic routing though, so you will need to do some research before you decide to go that path