I wanted to know when DHCP Server frees an offered (but not allotted) IP address and return it back to the address pool. Is there a time limit?
This happens when server doesn't receive the DHCPRequest message from the DHCP client that is offered an IP address.
Any idea?
Hello, I think that a possible answer to your question is the following:
DHCPREQUEST generated during SELECTING state:
Client inserts the address of the selected server in 'server identifier', 'ciaddr' MUST be zero, 'requested IP address' MUST be filled in with the yiaddr value from the chosen DHCPOFFER.
Note that the client may choose to collect several DHCPOFFER messages and select the "best" offer. The client indicates its selection by identifying the offering server in the DHCPREQUEST message. If the client receives no acceptable offers, the client may choose to try another DHCPDISCOVER message. Therefore, the servers may not receive a specific DHCPREQUEST from which they can decide whether or not the client has accepted the offer. Because the servers have not committed any network address assignments on the basis of a DHCPOFFER, servers are free to reuse offered network addresses in response to subsequent requests. As an implementation detail, servers SHOULD NOT reuse offered addresses and may use an implementation-specific timeout mechanism to decide when to reuse an offered address.
http://www.freesoft.org/CIE/RFC/2131/24.htm
According to rfc2131: "A server MAY choose to mark addresses offered to clients in
DHCPOFFER messages as unavailable. The server SHOULD mark an address offered to a client in a DHCPOFFER message as available if the server receives no DHCPREQUEST message from that client."
So, it would seem it depends on the platform as to whether or not a waiting period exists.
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