Wireless Access

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Access network design for branch, remote, outdoor and campus locations with Aruba access points, and mobility controllers.
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IP helper command on redundant controllers' VLAN interfaces

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  • 1.  IP helper command on redundant controllers' VLAN interfaces

    Posted Feb 04, 2015 07:40 PM

    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?


    #7210


  • 2.  RE: IP helper command on redundant controllers' VLAN interfaces
    Best Answer

    Posted Feb 04, 2015 07:43 PM

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



  • 3.  RE: IP helper command on redundant controllers' VLAN interfaces

    Posted Feb 04, 2015 07:51 PM

    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



  • 4.  RE: IP helper command on redundant controllers' VLAN interfaces

    Posted Feb 04, 2015 07:45 PM
    Do you have wireless clients on both controllers ?

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


  • 5.  RE: IP helper command on redundant controllers' VLAN interfaces

    Posted Feb 04, 2015 07:49 PM

    Hi Victor,

     

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