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DHCP Binding Entries - Two IP addresses for same MAC

Hello

I've configure DHCP on the 3560 switches and noticed that it is causing a lot of havoc on my NAC.

When I display the binding table, I noticed a leading 01 attached to the MAC address and the same MAC has two entries.

See the following example:

SW004-01#sh ip dhcp binding | include fb

10.120.4.80         001c.259b.fb10          Jan 04 2012 01:58 PM    Automatic

10.120.4.89         0100.1c25.9bfb.10       Jan 04 2012 01:59 PM    Automatic

10.120.4.97         b8ac.6f80.e960          Dec 27 2011 02:13 AM    Automatic

10.120.4.98         01b8.ac6f.80e9.60       Dec 30 2011 10:11 AM    Automatic

10.120.4.137        0024.e843.f644          Jan 04 2012 09:03 AM    Automatic

10.120.4.129        0100.24e8.43f6.44       Jan 04 2012 09:03 AM    Automatic

SW004-01#

I can not PING IPs mapped with the 12 digts MACs, but can PING IPs mapped to 14digts MACs (ARP still shows entries to 12 digts MACs).

What is happenting, the NAC receives a packet, 10.120.4.80, tries to connect to that IP to validate the host, but fails to connect as the host now has a new IP address for 10.120.4.89. It is causing massive false-positives on the NAC side.

Why is this happeing on the switch?

Two IP addresses are being leased to same host, and this will quickly exhaust my pool.

Is there a fix?

Thanks

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