[NTLUG:Discuss] DHCP

[Burton Strauss]

It should not be a problem as according to best practices per the RFC the
assigned address should be tested a couple of times to prevent conflict. 

But it's certainly not a good idea.  A badly implemented DHCP server could
choose not to perform the tests - SHOULD in RFC parlance isn't required.

http://www.faqs.org/rfcs/rfc2131.html

3.1 Client-server interaction - allocating a network address

...

   2. Each server may respond with a DHCPOFFER message that includes an
      available network address in the 'yiaddr' field (and other
      configuration parameters in DHCP options).  Servers need not
      reserve the offered network address, although the protocol will
      work more efficiently if the server avoids allocating the offered
      network address to another client.  When allocating a new address,
      servers SHOULD check that the offered network address is not
      already in use; e.g., the server may probe the offered address
      with an ICMP Echo Request.  Servers SHOULD be implemented so that
      network administrators MAY choose to disable probes of newly
      allocated addresses.  The server transmits the DHCPOFFER message
      to the client, using the BOOTP relay agent if necessary.

...

  5. The client receives the DHCPACK message with configuration
     parameters.  The client SHOULD perform a final check on the
     parameters (e.g., ARP for allocated network address), and notes the
     duration of the lease specified in the DHCPACK message.  At this
     point, the client is configured.  If the client detects that the
     address is already in use (e.g., through the use of ARP), the
     client MUST send a DHCPDECLINE message to the server and restarts
     the configuration process.  The client SHOULD wait a minimum of ten
     seconds before restarting the configuration process to avoid
     excessive network traffic in case of looping.


-----Burton


-----Original Message-----
From: discuss-bounces at ntlug.org [mailto:discuss-bounces at ntlug.org] On Behalf
Of Terry
Sent: Thursday, September 08, 2005 11:38 AM
To: NTLUG Discussion List
Subject: [NTLUG:Discuss] DHCP

Is this an accurate statement (pertaining to a Linux DHCP server presiding
over [mostly] MS PCs)?
 
"Having a system with a static IP assignment that is inside the range of
IPaddress' used by a DHC P server is not acceptable.  Reason being:
 If a new computer comes on-line, it may be issued that particular
IPaddress, and if so, there will be a problem.  This may never happen on a
small network. If there are only a handful of computers on the network (half
a dozen or so), you may never run into this sort of problem.  BUT, if and
when the network grows and gets to be fifty or a  hundred strong, sooner or
later, this problem will rear it's ugly head.  A computer will come on-line
and be issued an IP address that has been set as a static address to another
computer, .. . and then, later on, that other computer with the static IP
address will come on-line, and at that point they will both compete for
access that only one can have. During the competition neither of them will
get any access and only when one gives up will the other gain any bandwidth
or access to any outside networks. Fixed IPs should _only_ be assigned to IP
address that are outside the range used by the DHCP server."

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