Wireless Access

Frequent Contributor I

Multiple Subnets in a single VLAN?



We're looking to expand one of our wireless client networks so that we can handle more users.   The powers that be have decided that the best way of doing this is to overlay an additional subnet to the existing VLAN.  


The wireless client network is L3 & has an IP Assigned.  We perform captivate portal redirection for MAC Address Registration.  


So, say we have :


VLAN 645, with an IP Address of & a netmask of 


Let's say we'll add to this same VLAN the following subnet : w/ a netmask of  


What changes on the controller must I make for this to work?  Would I only have to add a route from the new network to the existing gateway or forwarding router address or will this all resolve itself in the router?







Re: Multiple Subnets in a single VLAN?

No!  This is a bad idea.  Can you just enable VLAN pooling on the VAP?

Seth R. Fiermonti
Consulting Systems Engineer - ACCX, ACDX, ACMX
Email: seth@hpe.com
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Frequent Contributor I

Re: Multiple Subnets in a single VLAN?

Thank you for your reply Seth, 


I don't believe that is possible…  I haven't been giving any specifics about the additional subnet, except that it was said it would be able to handle some 8000 addresses.  


I agree w/ you.  Everything I read about multiple subnets in a single VLAN (elsewhere i.e. Cisco) says that it is not a standard best practice, NOT RECOMMENDED, but possible.   I've opened a ticket w/ TAC, & I was told that the Aruba Controller (3600 v. does NOT support secondary IP Address assignements for VLAN interfaces.  


I don't know why they don’t just migrate to a new VLAN, or create a new one & pool it.  My guess is that we cannot (or will not) create the VLAN & that the plan is to eventually do away w/ the old network.   The hash that VLAN pooling utilizes to assign VLANs doesn't help us create a seamless migration.  As it is, I don’t think anything does; we'll have to simply swap the IP Address assigned to the existing VLAN & migrate our cp-redirect-address to a new address in the new subnet & wait for users to switch.  


I'm not certain if they were expecting this to be a clean, seamless, interruption-less, migration.  The more & more I find out, the more inclined I'm to suggest we announce an interruption of service.   I don't see anyway to implement this & test it w/o impacting users. 


I'm assuming that if we add the additional network to the VLAN, the wirless controller will recognize it.  ???  I also assume that clients will eventually join the new network once DHCP begins handing out addresses in that network.  ???  What I haven't gotten a definative answer on yet, is whether or not clients on this new network will be able to reach the cp-redirect-address on the old network in the same VLAN.  I don't know if a static route on my wireless controller may help w/ this, or if it simply will not work until we migrate off of the old network.  



Frequent Contributor II

Re: Multiple Subnets in a single VLAN?

If you really need 8192 addresses ( and are seeking to use a single vlan you are going to have a lot more issues (I doubt you will see any usable BW with this arrangement). There needs to be more of a design discussion here on why. If someone is unwilling to create more vlans to support the increase in users then there is bigger issues than wireless that needs to be addressed.


I do have several customers with multiple subnets per van. I've not been able to convince them this is a bad practice but they are wired vans and smaller subnets is the only reason they work at all. 


I would announce an outage and be done with it. 


I don’t think you should be waiting for users to switch. Make your changes on the controller for a new vlan/ip addresses and kick the users off forcing them to re-authenticate (getting the new subnet info as they reconnect) this will keep your outage shorter and less users complaints. 

David Dipert
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