dhcp server issues its own address

Simon Hobson dhcp1 at thehobsons.co.uk
Mon Apr 16 11:05:45 UTC 2007

S Kalyanasundaram wrote:

>    Just wanted a clarification, since there is no free lease it took 
>the abandon lease and issued. Since in the first time it is able to 
>identify the ip is exist in the network by pinging, why cant it do 
>in the next time. Abandon the IP again and say no free lease again. 
>Why the reclaimed address is not followed as like other free lease, 
>it just issued with out any check like what is done earlier?
>Is there any time gap to reclaim the abandoned  IP address?

These are questions for someone like Ted or David who understand the 
internals of the program. My guess (note: GUESS) is that the path 
through the code to reclaim an abandoned lease somehow bypasses the 
'ping before offer' check, or perhaps the ping/it's reply got lost, 
or ?

I'm not aware of any specific timing constraints on abandoning or 
reclaiming leases - but abandoned leases are only ever reclaimed when 
there are no other available addresses. The order for picking an 
address is :

- Addresses that have never been used before. Issued in an 
implementation dependent order, currently 'top down' but not 
documented and liable to change without warning.

- Addresses which have been used before but are now free (lease has 
expired or has been explicitly released by client). Issued on "least 
recently used" basis.

- Abandoned addresses (ie have a lease record marked as abandoned).

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