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What happened if DHCP not available ?

    Question

  • HI, I have a question:

    I have one DHCP Server (Windows 2003) and XP clients.

    The DHCP Server have 20 days DHCP lease configurated.

    If a DHCP Server is not available and XP client is in 20% lease time...

    What happened with this PC ?

    Keep your IP and continue work or get APIPA?

     Thanks for all and excuse my bad English

    Friday, September 02, 2011 11:40 AM

Answers

  • Hello,

    each DHCP client will try to update after 50% lease time the lease with the DHCP server, if the DHCP server doesn't react it tries again after the next 50% of the remaining lease time and so on. If then still no DHCP server is available you run into problems.

    But with 20 days this shouldn't happen.

     


    Best regards Meinolf Weber Disclaimer: This posting is provided "AS IS" with no warranties or guarantees , and confers no rights.
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:28 AM
    Friday, September 02, 2011 11:49 AM
  • So, each DHCP client tries to renew its lease after 50% time of lease. If it couldn't conntact to DHCP server within that time, it tries once again after 87,5% time of lease. If connection also wasn't possible it uses IP address to 100% lease time and after that tries to connect DHCP server. If connection won't be possible it will use APIPA, if connection would be possible, it gets IP address (but then it doesn't have to be the same address - becuase after 87,5% lease time it was not renewed and other client migt have got it).

    In your case it looks this way:

    1) client gets IP address lease for 20 days

    2) after 10 days it tries to renew its address

    3) let's say that it was not possible, then after (about) 18 days retries renewal

    4) if no connection was possible it uses address for another 2 days

    5) after 100% time DHCP discover and request is send again

    6) if connection to DHCP server is possible then new IP is issued; if not then APIPA

    But if your DHCP server will be down longer than 20 days you will see that and react to fix it (belive me) :)

    Besides that, no new clients will be able to obtain IP address lease


    Regards, Krzysztof ---- Visit my blog at http://kpytko.wordpress.com
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:28 AM
    Friday, September 02, 2011 12:07 PM
  • Hello Zidac,

    Additional comments to validate your concern...

    "If a DHCP Server is not available and XP client is in 20% lease time...What happened with this PC ?"  The PC's IP address will remain on the system until the lease is expired.  Just because a DHCP server is unailable, it does not mean that all of the active leases are invalid.  The PC will not use an APIPA address until it is unable to renew the lease.

    Its a good idea to set up another DHCP server and split the scopes 50/50.  In this scenario, if a DHCP server fails, you have more time to repair the DHCP server before your leases all expire.

     


    Visit anITKB.com, an IT Knowledge Base.

    anITKB facebook youtube
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:29 AM
    Friday, September 02, 2011 2:13 PM
  • Hi Zidac,

     

    Thanks for posting here.

     

    A few design options in the article below will also help to consolidate DHCP service:

     

    Design Options for DHCP Availability and Fault Tolerance

    http://technet.microsoft.com/en-us/library/dd296672(WS.10).aspx

     

    Thanks.

     

    Tiger Li


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:29 AM
    Monday, September 05, 2011 9:01 AM

All replies

  • Hello,

    each DHCP client will try to update after 50% lease time the lease with the DHCP server, if the DHCP server doesn't react it tries again after the next 50% of the remaining lease time and so on. If then still no DHCP server is available you run into problems.

    But with 20 days this shouldn't happen.

     


    Best regards Meinolf Weber Disclaimer: This posting is provided "AS IS" with no warranties or guarantees , and confers no rights.
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:28 AM
    Friday, September 02, 2011 11:49 AM
  • So, each DHCP client tries to renew its lease after 50% time of lease. If it couldn't conntact to DHCP server within that time, it tries once again after 87,5% time of lease. If connection also wasn't possible it uses IP address to 100% lease time and after that tries to connect DHCP server. If connection won't be possible it will use APIPA, if connection would be possible, it gets IP address (but then it doesn't have to be the same address - becuase after 87,5% lease time it was not renewed and other client migt have got it).

    In your case it looks this way:

    1) client gets IP address lease for 20 days

    2) after 10 days it tries to renew its address

    3) let's say that it was not possible, then after (about) 18 days retries renewal

    4) if no connection was possible it uses address for another 2 days

    5) after 100% time DHCP discover and request is send again

    6) if connection to DHCP server is possible then new IP is issued; if not then APIPA

    But if your DHCP server will be down longer than 20 days you will see that and react to fix it (belive me) :)

    Besides that, no new clients will be able to obtain IP address lease


    Regards, Krzysztof ---- Visit my blog at http://kpytko.wordpress.com
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:28 AM
    Friday, September 02, 2011 12:07 PM
  • Hello Zidac,

    Additional comments to validate your concern...

    "If a DHCP Server is not available and XP client is in 20% lease time...What happened with this PC ?"  The PC's IP address will remain on the system until the lease is expired.  Just because a DHCP server is unailable, it does not mean that all of the active leases are invalid.  The PC will not use an APIPA address until it is unable to renew the lease.

    Its a good idea to set up another DHCP server and split the scopes 50/50.  In this scenario, if a DHCP server fails, you have more time to repair the DHCP server before your leases all expire.

     


    Visit anITKB.com, an IT Knowledge Base.

    anITKB facebook youtube
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:29 AM
    Friday, September 02, 2011 2:13 PM
  • Hi Zidac,

     

    Thanks for posting here.

     

    A few design options in the article below will also help to consolidate DHCP service:

     

    Design Options for DHCP Availability and Fault Tolerance

    http://technet.microsoft.com/en-us/library/dd296672(WS.10).aspx

     

    Thanks.

     

    Tiger Li


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.
    • Marked as answer by Tiger Li Thursday, September 08, 2011 7:29 AM
    Monday, September 05, 2011 9:01 AM