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APs unable to automatically receive IP address from DHCP

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  • 1.  APs unable to automatically receive IP address from DHCP

    Posted 26 days ago
    I am starting a new thread for this issue as the community helped me determine that my previous understanding of this issue was mistaken.

    Recently, all the APs on our networks have been unable to receive a valid IP address from the correct Vlan when plugged into ethernet or after being provisioned. I have been working around this issue by plugging downed APs into the console, interrupting the boot sequence, running the "dhcp" command, saving the good IP address.

    I thought I was purging a bad IP address and saving good DHCP settings, but I now realize I have essentially just been using the console to statically assign the APs an IP from the correct Vlan.

    I'm not sure why DHCP has stopped working correctly. It seems to be "half" working as the console workaround does receive a valid IP from DHCP. It just must be saved manually as a static address.

    I'd really like to keep the APs on DHCP and allow them to renew from the address pool as needed. I can make reservations on the addresses but it is my understanding that this is not the recommended practice for managing APs.

    DHCP is not configured on the Aruba controller, but is provided externally. The only changes that have been made on our network is that I upgraded our DCs and in the process migrated the DHCP server on one of our VLANs to a new IP address. I also created a load-balancing/failover relationship between the upgraded DCs that previously did not exist. 

    Here are the specifics of what is happening:

    1.Plug the AP in. It receives an IP from VLAN 2-10.0.0.0 network. APs do not come up on this VLAN. (VLAN 2 is where the DC upgrades took place)
    2. Plug the AP into the console and interrupt the boot sequence, run "dhcp", save the address with "save" and then boot. AP comes up with an IP from VLAN 50--10.50.0.0 network. This VLAN is running a DHCP server on a different device and service than VLAN 2.

    Last question, that maybe a bit a non-sequitur. Can anyone tell me if the default loopback address for an Aruba controller is the controller's master address? I don't think this issue is related to rule 43 in DHCP options, but I would still like to configure it correctly.

    Thank you so much!


  • 2.  RE: APs unable to automatically receive IP address from DHCP

    Posted 24 days ago
    Do you have two dhcp servers running at the same time on that layer 2 VLAN?  I would do a packet capture of the wired interface of that AP to get to the bottom of what is going on.

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    Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
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  • 3.  RE: APs unable to automatically receive IP address from DHCP

    Posted 24 days ago
    Thank you very much for these suggestions.

    I did create a load-balancing/failover relationship between the primary and secondary DC on VLAN 2. So I guess, technically, yes, there are two DHCP servers running, but the configuration is identical. 

    Can you recommend the best way to do a packet capture on the wired interface of the AP? Would Is there a way to use wireshark simultaneously with a console session?

    Thanks again.


  • 4.  RE: APs unable to automatically receive IP address from DHCP

    Posted 24 days ago
    Maybe you can try connect yor PC to same ethernet port. And troubleshoot if you are not able to receive IP address. And also you can use wireshark.

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    Tuna AKYOL
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  • 5.  RE: APs unable to automatically receive IP address from DHCP

    Posted 23 days ago
    Do the dhcp servers give out overlapping ip addresses? Either way, if you mirror the port on the switch that the AP is on, you might be able to obtain a packet capture to understand what could be going on.  No need to do the console at the same time, for now...

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    Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
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  • 6.  RE: APs unable to automatically receive IP address from DHCP

    Posted 23 days ago
      |   view attached
    @Tuna: A laptop does receive the proper IP address from the correct VLAN when plugged into the wall port that the AP is plugged into.

    @cjoseph: The DHCP servers are running an identical config. All configs are the same including the scope and lease durations. Primarily, I set this up for redundancy. In case one of the servers goes, the other will continue to renew and assign valid IPs.

    Check out this packet capture that is filtered by DHCP. If anyone can help me interpret what is going on here, I'd be much obliged. It looks like the AP is receiving ACKs from .88 and NAKs from .25. 

    XXX.XXX.XXX.25 and XXX.XXX.XXX.88 are the IP addresses of the ​two DC's running DHCP.

    Again, both of these DHCP servers are on VLAN 2. APs only seem to be coming up on IPs assigned from VLAN 50 (DHCP is assigned by a totally different service on this VLAN.)

    I also have a src.mac filter if that would be helpful.​

    Thanks, all.


  • 7.  RE: APs unable to automatically receive IP address from DHCP

    Posted 22 days ago
    For testing purposes, I deleted the failover relationship between the primary and secondary DCs on the VLAN that is handing out stale addresses (VLAN 2). Still no luck. AP gets an AP from this VLAN, has power and ethernet but never broadcasts.  

    Again, if I interrupt the boot sequence in the console, and run DHCP I get an IP from VLAN 50 I save the address (making it static) and the AP works fine.

    Perplexed. Dumbfounded. Stumped.


  • 8.  RE: APs unable to automatically receive IP address from DHCP

    Posted 21 days ago
    Honestly, having 2 dhcp servers  creates issues that you wouldn't have normally.  You are jumping through too many hoops just to get APs up and running. To  me it is not worth it....

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    Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
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  • 9.  RE: APs unable to automatically receive IP address from DHCP

    Posted 21 days ago
    I hear you. That is why I deleted the failover relationship on the second server. Even with just one DHCP server running, the issue is happening.....


  • 10.  RE: APs unable to automatically receive IP address from DHCP

    Posted 21 days ago

    I think, maybe there is a reserved ip for this AP's mac address on DHCP server. And you should configure AP port to access vlan 2. If AP's port untagged vlan 2, it should not receive ip address from vlan 50

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    Tuna AKYOL
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  • 11.  RE: APs unable to automatically receive IP address from DHCP

    Posted 21 days ago
    Thanks for your continued support here. Here's what I can tell you:

    1. There are no reservations for on our DHCP server. 
    2. I've tested the switchport settings. I've placed the switchport in access mode for VLAN 2. Same issue results. When I place the switchport in access mode for VLAN 50, the AP comes online but only broadcasts VLAN 50. That is why the switchport is a trunk port. It needs to pass both VLANs through to the AP once a good IP has been assigned. At least, this is what I think...

    Why this would start happening all of the sudden is the big question for me right now.

    Thanks again for all your help.