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Cisco ASA and Win2K3 Server R2 Standard DHCP Server

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  • Cisco ASA and Win2K3 Server R2 Standard DHCP Server

    We currently have Cisco ASA 5505 working as a DHCP server. But, sometimes it takes some time to give IP address to new clients, so I would like to switch that DHCP Server to our DC. I want to use the same range that is currently in use. My plan was to setup DHCP Server on Win2k3, with range, DNS and all other options, than to switch off the DHCP on ASA, and switch on the DHCP on Win2K3. My question is will the DHCP on Win2k3 know that some addresses are already in use, and that it will give new, unused addresses? I always have like 20-30 used, or occupied IPs in that range.

    Thanks in advance, and sorry if I put this topic in the wrong forum, didn't know if it should go here or in general networking, or in Cisco PIX/ASA part

  • #2
    Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

    >My question is will the DHCP on Win2k3 know that some addresses
    >are already in use, and that it will give new, unused addresses?

    Answer is NO. After switching the DHCP to your D, please restart all the clients which has obtained IP address earlier from ASA. That leaves you clean.

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    • #3
      Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

      Originally posted by charlsteve View Post
      >My question is will the DHCP on Win2k3 know that some addresses
      >are already in use, and that it will give new, unused addresses?

      Answer is NO. After switching the DHCP to your D, please restart all the clients which has obtained IP address earlier from ASA. That leaves you clean.
      Thanks, I was hoping that wouldn't be needed..
      Last edited by Highl1; 7th July 2009, 11:05.

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      • #4
        Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

        I think atleast you can do ipconfig /release{renew} on these 20-30 machines.

        Another odd alternative is, identify all 20 IPs and restrict them in DHCP from issuing(not sure where that option is; but it should be there to restrict/reserve few IPs). Once the 20 machines completes their lease period, they will try to renew the IP address and fail for the first time as ASA is no more offering the IP and will sendout a new DHCP discover request over network and this time your DC responds to issue IP address.

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        • #5
          Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

          Originally posted by charlsteve View Post
          I think atleast you can do ipconfig /release{renew} on these 20-30 machines.

          Another odd alternative is, identify all 20 IPs and restrict them in DHCP from issuing(not sure where that option is; but it should be there to restrict/reserve few IPs). Once the 20 machines completes their lease period, they will try to renew the IP address and fail for the first time as ASA is no more offering the IP and will sendout a new DHCP discover request over network and this time your DC responds to issue IP address.
          Yes, I can make an exclude range and forbid those addresses for some time. Thanks a lot!

          Comment


          • #6
            Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

            Leave the credit if my solution works for you

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            • #7
              Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

              Actually, you can enable conflict detection on your Windows DHCP Server, which will try to contact an IP address several times before it gives out the lease to a new client. It ensures that no other computer with that IP address exists before the lease is given out.

              http://technet.microsoft.com/en-us/l...8WS.10%29.aspx

              After enabling this, remove DHCP from your ASA and you are golden.

              I've done this in the past and it works well for me.
              MCITP:SA, MCSA 2003, MCP, CCNA, A+, Net+, Security+

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              • #8
                Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

                Originally posted by boondock View Post
                Actually, you can enable conflict detection on your Windows DHCP Server, which will try to contact an IP address several times before it gives out the lease to a new client. It ensures that no other computer with that IP address exists before the lease is given out.

                http://technet.microsoft.com/en-us/l...8WS.10%29.aspx

                After enabling this, remove DHCP from your ASA and you are golden.

                I've done this in the past and it works well for me.
                Thanks, this is much better solution than excluding 30-40 addresses.

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                • #9
                  Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

                  Once you trn off the DHCP server on the ASA box and clients broadcast for an address it will get the address from the 2k3 server.

                  But as boondock says turn on conflict detection and you'll be good to go.

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                  • #10
                    Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

                    As "wullieb1" said I think we need to ....

                    o Turn off DHCP on ASA fist
                    o Turn ON DHCP in W2K3 next
                    o Enable conflict detection last

                    This serves the purpose. You will never come out ASA DHCP until you disable it first. Corrections are welcome

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                    • #11
                      Re: Cisco ASA and Win2K3 Server R2 Standard DHCP Server

                      Sorry I didn't reply earlier. Everything went smooth, setup the DHCP on Win2K3, switch off ASA DHCP, enable scope on Win2k3 DHCP with conflicts enabled, and everything worked like a charm.

                      Thanks a lot guys!

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