Q177204: DHCP Does Not Offer Addresses in Numerical Sequence
Article: Q177204
Product(s): Microsoft Windows NT
Version(s): WinNT:3.5,3.51,4.0
Operating System(s):
Keyword(s): kbnetwork kbinfo kbArtTypeINF
Last Modified: 10-AUG-2001
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0
-------------------------------------------------------------------------------
SUMMARY
=======
Microsoft Windows NT Dynamic Host Configuration Protocol (DHCP) server offers IP
lease information to DHCP clients on the network. Your DHCP Server may appear to
be randomly selecting addresses to offer to DHCP clients. This article discusses
the method that DHCP server uses to assign addresses.
MORE INFORMATION
================
DHCP server maintains two lists of address blocks as follows:
- partially filled in-use
- totally used
Each of the above type of block consists of 32 addresses.
For additional information, please see the following article in the Microsoft
Knowledge Base:
ARTICLE-ID: Q151696
TITLE : Extending DHCP Start Address
Partially filled in-use, or in-use blocks, provide addresses for the next DHCP
request from DHCP clients. If this block runs out of addresses (no more
addresses available to lease), a new block is created and added to the front of
the in-use list with one address taken off for the currently requesting client.
Totally used, or used blocks, are blocks that have no IP addresses available to
be leased.
NOTE: Exclusion ranges and reservations will always be in either the in- use
blocks or the used blocks.
When an in-use block gets completely leased, it is added to the end of the used
list. If all the addresses of a used block get released so that the block is
totally free, the block is deleted from the used list. A block that is not
present in either of the lists is assumed to be totally free.
For example, a scope of 200.10.10.0, which has a range from 200.10.10.1 to
200.10.10.254 is used in the following manner:
1. The first block would have the following addresses:
200.10.10.1 - 200.10.10.32
2. When the first address is requested, this block is considered an in- use
block. When the block is completely leased out, it is considered a used
block.
3. When the next address is requested, a second block, 200.10.10.33 -
200.10.10.64, is created. 200.10.10.33 is handed out and the block is added
to the front of the in-use list.
4. When this second block gets completely leased, it is moved to the end of the
used list (after the first used block).
5. Upon another request, the 200.10.10.65 - 200.10.10.96 block is created,
handing out 200.10.10.65 and adding the new block to the front of the in-use
list.
At this point, the in-use and used lists appear similar to the following:
in-use used (completely leased)
------ ------------------------
200.10.10.65 - 200.10.10.96 (.65 leased) 200.10.10.1 - 200.10.10.32
200.10.10.33 - 200.10.10.64
6. If 200.10.10.63 is released, the .33 - .64 block is moved back to the in-use
list and the lists look similar to the following:
in-use used (completely leased)
------ ------------------------
200.10.10.65 - 200.10.10.96 (.65 leased) 200.10.10.1 - 200.10.10.32
200.10.10.33 - 200.10.10.64 (.63 available)
7. If all the addresses from 200.10.10.33 - 200.10.10.64 are released except .64
and all the addresses from 200.10.10.1 - 200.10.10.32 are released except
.32, the lists look similar to the following:
in-use used (completely leased)
------ ------------------------
200.10.10.65 - 200.10.10.96 (.65 leased)
200.10.10.33 - 200.10.10.64 (.64 leased)
200.10.10.1 - 200.10.10.32 (.32 leased)
Now the following ranges or addresses are free:
200.10.10.1 - 200.10.10.31
200.10.10.33 - 200.10.10.63
200.10.10.66 - 200.10.10.254
Looking at the in-use blocks above, you can see that the next address that
will be offered from this DHCP server will be 200.10.10.66.
======================================================================
Keywords : kbnetwork kbinfo kbArtTypeINF
Technology : kbWinNTsearch kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version : WinNT:3.5,3.51,4.0
Issue type : kbinfo
=============================================================================
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 1986-2002.