Wireless Access

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Occasional Contributor II
Posts: 12
Registered: ‎01-16-2015

IP helper command on redundant controllers' VLAN interfaces

Good day,

 

Getting a little farther with configuring our two new 7210 controllers to take traffic.  I am now at the point when I need to settle DHCP for wireless clients.  ArubaOS 6.4 limits the number of IPv4 addresses it will serve in its DHCP server to 5210 (or something close to that).  But, that is insufficient.  We have enough subnetworks to exceed that number of addresses.

 

Our routing scheme is such that the gateway router interface for each of the wireless client VLANs is not either of the controllers, but is an ASA.

 

So, we've decided to use a dedicated DHCP server.  Now, I finally get to the question:

 

We have redundant controllers, as I said.  I don't foresee a problem with adding, for example, the identical IP helper command on the VLAN 403 in each redundant controller.  When a client comes up on that subnetwork, one of those two controller VLAN interfaces is going to hear the DHCP request broadcast first, and get an address from the DHCP server.  I think the DHCP server will simply ignore the second DHCP request for that host.

 

At least, this is what I think will happen.

 

Does anyone here see a potential problem with this configuration?

Guru Elite
Posts: 8,633
Registered: ‎09-08-2010

Re: IP helper command on redundant controllers' VLAN interfaces

Correct, shouldn't be any issues but if the layer 3 interface (user default gateway) is upstream, I would add the helper-address there.


Tim Cappalli | Aruba Security TME
@timcappalli | timcappalli.me | ACMX #367 / ACCX #480
MVP
Posts: 4,301
Registered: ‎07-20-2011

Re: IP helper command on redundant controllers' VLAN interfaces

Do you have wireless clients on both controllers ?

If so ,are you using the same segment/VLAN on each controller ?
Thank you

Victor Fabian
Lead Mobility Engineer @ Integration Partners
AMFX | ACMX | ACDX | ACCX | CWAP | CWDP | CWNA
Occasional Contributor II
Posts: 12
Registered: ‎01-16-2015

Re: IP helper command on redundant controllers' VLAN interfaces

Hi Victor,

 

Yes, there will be clients on both controllers, and the user VLANs appear on both controllers.

Occasional Contributor II
Posts: 12
Registered: ‎01-16-2015

Re: IP helper command on redundant controllers' VLAN interfaces

Thanks, TIm.

 

I've been mulling that over, too.  I will only have a single DHCP sever, as well as that single ASA acting as the gateway router for the user VLANs.  So, there will already be single points of failure.  This configuration is only for guest users, though.  However, since there are single points of failure on the way to the internet, perhaps it is probably simpler to put that DHCP forwarding command on that ASA.

 

Jess

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