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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Define a Source Interface for DHCP Requests?

  • 1.  Define a Source Interface for DHCP Requests?

    Posted Aug 02, 2018 07:07 PM

    Working with a customer who is having trouble getting DHCP to work for user VLAN 94. It appears the controller is sourcing the DHCP request from it's management VLAN 93. VLAN 93 and VLAN 94 are on seperate physical ports and we have IP helpers on both VLAN Interfaces. The customers Firewall is blocking because of the management VLAN 93 should not be sending DHCP requests - Is there a way to force DHCP requests for VLAN 94 to use the VLAN 94 interface?

     

    Any ideas why it's not? I was thinking about removing the IP Helpers and the IP interface for the VLAN 94 to make it simple L2 connectivity, but not sure if that's the right path.



  • 2.  RE: Define a Source Interface for DHCP Requests?

    Posted Aug 02, 2018 09:28 PM

    You cannot define a source interface for dhcp packets.  The DHCP source interface/ip address is the northbound (egress) interface of the controller, otherwise your DHCP server would not know how to deliver it back to the controller.



  • 3.  RE: Define a Source Interface for DHCP Requests?

    Posted Aug 03, 2018 06:01 AM

    Acctually I remember upgrading to Aruba OS 6.2 I think Aruba changed the behaviour of sourcing the DHCP packets to be the recipient interface of the DHCP discover. I remember it since it caused a large incident at one of my customers when upgrading and the solution was to implement correct routing for the DHCP server to find its way back to the client subnet (the recipient interface of the controller in this case).

     

    So according to me it should source with your recipient interface. I haven't tested it since then so I can´t say for sure, perhaps it´s been changed again.

     

    Which version are you running?

     

    Cheers,



  • 4.  RE: Define a Source Interface for DHCP Requests?

    Posted Aug 03, 2018 06:57 AM

    Christoffer,

     

    A change was made in the distant past, but changed back fairly quickly to what it is right now.



  • 5.  RE: Define a Source Interface for DHCP Requests?

    Posted Aug 03, 2018 07:32 AM

    Thanks for clearing that up @cjoseph :)

     

    Topic maker:

    I guess this means your setup is working as intended. Allow that IP to send DHCP requests through the firewall would be the easiest way to make your setup work.

     

    Cheers,