duplicate mac addresses requesting dhcp server

Simon Hobson dhcp1 at thehobsons.co.uk
Wed Oct 18 10:28:09 UTC 2006

Gilbert Coles wrote:

>With this question I meant that if the dhcp server has already served a mac1
>with ip1 (so there's an entry with mac1:ip1 in the dhcp.leases file) and
>another pc2 with its mac spoofed to mac1 comes along and asks the dhcp
>server for an IP, will the dhcp server (before assigning an IP to pc2) check
>in the leases file to see if it already assigned an ip to mac1?

Yes, it will look in the leases file, find an existing lease, and 
simply extend it. To the server, there is likely to be little (if 
anything) to differentiate between pc2 and pc1 simply checking it's 
address is still valid after (for example) waking from sleep.

Unless they supply different Client-IDs, then pc1 and pc2 are the 
SAME client as far as the server is concerned - it has no way 
whatsoever of detecting such duplicate MACs.

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