Announcement

Collapse
No announcement yet.

DHCP not allocating properly

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • DHCP not allocating properly

    Hi

    the range I have on the single forest root server is to assign address from 172.18.176.1 - 172.18.176.200

    I have no more then 140 devices on the network all counted, however after looking through the address leases i was alarmed to notice that there have been 190 address assigned, after closer inspection i see the leases start at 1 and go in uniform or order to 122 then there is a big jump to 148 and then a jump to 180, so there has been NO allocation of 125 - 147 and NO allocation of 160 upwards, I can confirm there are no reservations,

    I have deleted all the leases but next day i check and still the big jumps are there to see

    cant understand why there are big jumps, and now i am worried that ill run out of avaliable address, when 200 is ample ...

    cheers in advanced

  • #2
    Re: DHCP not allocating properly

    do a cleanup on the database

    I think it's called reconcile, off the top of my head
    Please do show your appreciation to those who assist you by leaving Rep Point https://www.petri.com/forums/core/im.../icon_beer.gif

    Comment


    • #3
      Re: DHCP not allocating properly

      What's your current lease time?
      Your clients will try to re-request there current lease if it's still valid in there lease time so sounds like nothing to worry...

      It's all in the DHCP RFC. I can't stress it enough, read the RFC's. They are there for a reason.
      It's only 45 pages, yet if you read it, you'll gonna understand how DHCP does it's job.

      Just look at this figure (if it fits )

      Code:
      RFC 2131          Dynamic Host Configuration Protocol         March 1997
      
      
       --------                               -------
      |        | +-------------------------->|       |<-------------------+
      | INIT-  | |     +-------------------->| INIT  |                    |
      | REBOOT |DHCPNAK/         +---------->|       |<---+               |
      |        |Restart|         |            -------     |               |
       --------  |  DHCPNAK/     |               |                        |
          |      Discard offer   |      -/Send DHCPDISCOVER               |
      -/Send DHCPREQUEST         |               |                        |
          |      |     |      DHCPACK            v        |               |
       -----------     |   (not accept.)/   -----------   |               |
      |           |    |  Send DHCPDECLINE |           |                  |
      | REBOOTING |    |         |         | SELECTING |<----+            |
      |           |    |        /          |           |     |DHCPOFFER/  |
       -----------     |       /            -----------   |  |Collect     |
          |            |      /                  |   |       |  replies   |
      DHCPACK/         |     /  +----------------+   +-------+            |
      Record lease, set|    |   v   Select offer/                         |
      timers T1, T2   ------------  send DHCPREQUEST      |               |
          |   +----->|            |             DHCPNAK, Lease expired/   |
          |   |      | REQUESTING |                  Halt network         |
          DHCPOFFER/ |            |                       |               |
          Discard     ------------                        |               |
          |   |        |        |                   -----------           |
          |   +--------+     DHCPACK/              |           |          |
          |              Record lease, set    -----| REBINDING |          |
          |                timers T1, T2     /     |           |          |
          |                     |        DHCPACK/   -----------           |
          |                     v     Record lease, set   ^               |
          +----------------> -------      /timers T1,T2   |               |
                     +----->|       |<---+                |               |
                     |      | BOUND |<---+                |               |
        DHCPOFFER, DHCPACK, |       |    |            T2 expires/   DHCPNAK/
         DHCPNAK/Discard     -------     |             Broadcast  Halt network
                     |       | |         |            DHCPREQUEST         |
                     +-------+ |        DHCPACK/          |               |
                          T1 expires/   Record lease, set |               |
                       Send DHCPREQUEST timers T1, T2     |               |
                       to leasing server |                |               |
                               |   ----------             |               |
                               |  |          |------------+               |
                               +->| RENEWING |                            |
                                  |          |----------------------------+
                                   ----------
                Figure 5:  State-transition diagram for DHCP clients
      Last edited by Dumber; 13th September 2011, 17:06.
      Marcel
      Technical Consultant
      Netherlands
      http://www.phetios.com
      http://blog.nessus.nl

      MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
      "No matter how secure, there is always the human factor."

      "Enjoy life today, tomorrow may never come."
      "If you're going through hell, keep going. ~Winston Churchill"

      Comment


      • #4
        Re: DHCP not allocating properly

        current lease time is 8days standard

        Thanks guys, Ill first do the reconcile of the DHCP database by tehcamel and then read the diagram and the RFC DHCP notes, yea 45 pages of reading.
        looks ALOT more in depth than just the DORA process, ha..

        cheers

        Comment


        • #5
          Re: DHCP not allocating properly

          Lol, 45 pages is nothing but it will answer all you're questions about DHCP.
          Also, with 8 days, you're client will re-request it's IP address.

          Especially this part help you're question out

          the client may suggest values for the network address
          and lease time in the DHCPDISCOVER message. The client may include
          the 'requested IP address' option to suggest that a particular IP
          address be assigned,
          and may include the 'IP address lease time'
          option to suggest the lease time it would like.

          And:
          http://technet.microsoft.com/en-us/l.../cc958935.aspx
          Requesting

          After a DHCP client has received a DHCPOffer message from a DHCP server, the client moves into the Requesting state. The DHCP client knows the IP address it wants to lease, so it broadcasts a DHCPRequest message to all DHCP servers. The client must use a broadcast because it still does not have an assigned IP address. Figure 4.7 shows the Requesting state.

          If the IP address of the client was known (that is, the computer restarted and is trying to lease its previous address), the broadcast is looked at by all of the DHCP servers. The DHCP server that can lease the requested IP address responds with either a successful acknowledgment (DHCPAck) or an unsuccessful acknowledgment (DHCPNak). The DHCPNak message occurs when the IP address requested is not available or the client has been physically moved to a different subnet that requires a different IP address. After receiving a DHCPNak message, the client returns to the Initializing state and begins the lease process again.

          If the IP address of the client was just obtained with a DHCPDiscover or DHCPOffer exchange with a DHCP server, the client puts the IP address of that DHCP server in the DHCPRequest. The specified DHCP server responds to the request, and any other DHCP servers retract their DHCPOffer. This ensures that the IP addresses that were offered by the other DHCP servers go back to an available state for another DHCP client.
          Again, no worries are there to be made. No reconcile or any other form of action is needed.
          Last edited by Dumber; 13th September 2011, 19:45.
          Marcel
          Technical Consultant
          Netherlands
          http://www.phetios.com
          http://blog.nessus.nl

          MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
          "No matter how secure, there is always the human factor."

          "Enjoy life today, tomorrow may never come."
          "If you're going through hell, keep going. ~Winston Churchill"

          Comment


          • #6
            Re: DHCP not allocating properly

            Have a look in DHCP and see if there is more than 1 address being assigned to a single machine.
            1 1 was a racehorse.
            2 2 was 1 2.
            1 1 1 1 race 1 day,
            2 2 1 1 2

            Comment


            • #7
              Re: DHCP not allocating properly

              you should give one static IP to the machine in advance options and then click automatic IP address! this will solve your problem.

              Comment


              • #8
                Re: DHCP not allocating properly

                Managing and maintaining 140 static IPs will be far more of a hassle than sorting a possible DHCP problem. Next you will be suggesting scrapping DNS and using a HOSTS file
                Tom Jones
                MCT, MCSE (2000:Security & 2003), MCSA:Security & Messaging, MCDBA, MCDST, MCITP(EA, EMA, SA, EDA, ES, CS), MCTS, MCP, Sec+
                PhD, MSc, FIAP, MIITT
                IT Trainer / Consultant
                Ossian Ltd
                Scotland

                ** Remember to give credit where credit is due and leave reputation points where appropriate **

                Comment

                Working...
                X