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DHCP not working

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Posts: 23
4232     0

Hi All, 

 

I am new to Infoblox, just started with DHCP configuration a virtual 1425 appliance.

I am unable to get DHCP running -the end  device cannot obtain and IP address.However, I can see the below messages in  syslog:

 

2018-07-25T16:54:02+00:00 daemon infobloxtst.bcg.com dhcpd[47333]: info DHCPDISCOVER from 88:43:e1:c6:8c:6e via eth1 TransID 1b763e22


2018-07-25T16:54:02+00:00 daemon infobloxtst.bcg.com dhcpd[47333]: info DHCPREQUEST for 10.223.45.0 (10.91.32.52) from 88:43:e1:c6:8c:6e via eth1 TransID 1b763e22: unknown lease 10.223.45.0.


2018-07-25T16:54:03+00:00 daemon infobloxtst.bcg.com dhcpd[47333]: info DHCPOFFER on 10.223.44.255 to 88:43:e1:c6:8c:6e (SEP8843E1C68C6E) via eth1 relay eth1 lease-duration 119 offered-duration 28800

 

 

So  10.91.32.52 is theold DHCP server IP address,  I have removed the config related to this IP already but it still shows up in the logs not sure why.I see there is a DHCPDISCOVER message that comes through but no final IP address assignment.Any inputa on what is wrong here?

 

Regards,

Kirti

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Re: DHCP not working

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Community Manager
Community Manager
Posts: 356
4232     0

Assuming that the DHCP server is set as authoritative, what should happen in this case is the following:

 

  1. Client attempts to renew its (now invalid) IP address by sending a request (unicast) to its DHCP server.
  2. If this times out, the client will resend the request as a broadcast.
  3. When the DHCP server is set as authoritative, it will respond with a "decline" (otherwise, it will ignore the request).
  4. The client will start over by sending DHCP discover (broadcast).
  5. The DHCP server will respond with an offer.
  6. The client will 'request' the address from the DHCP server.
  7. The DHCP server will respond with a 'DHCP ack'.

 

From the log snippet that you provided, we can see that most likely, steps 1-5 are taking place. What we can't see is if the client is following up with the expected request for the offered IP. It would be helpful to run a network sniffer (Wireshark?) on the client side while testing this out and verify:

 

  1. That the client is receiving the offer from the DHCP server.
  2. That the client is sending out that request.

 If the client never receives the offer, or it does and sends request but that is not received by the DHCP server, that would indicate a network issue where these packets are being blocked/lost somewhere on the network. Things to check would include firewalls/network security devices, and/or IP helpers/relay agents.

 

If the client receives the offer but never attempts to send the request, it may be that a DHCP option the client requires was not configured.

 

Hope this helps.

 

Regards,

Tony

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Re: DHCP not working

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Posts: 23
4232     0

Hi , 

 

So what was happening was, the client was not giving up the old IP provided by the old DHCP server even after I removed the helper-address command.I had to disable the scopes off the old DHCP server and that is when the client got an IP address from the new DHCP Server (Infoblox).

Thanks for your assistance!

 

Regards,

Kirti

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