DHCP Binding Entries - Two IP addresses...

Cisco Support Community

Community Member

‎12-05-2011 11:24 AM

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

Labels:

Network Management

Latest Documents

BGP Conditional Advertisement Feature

Created by Dennis Mink on 03-06-2018 09:17 PM

This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does "Th... view more

le router cisco 887 VA-K9 ne diffuse pas les adresses IP au reseau local

Created by mustiman on 03-05-2018 05:53 AM

Question bonjours j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m... view more

command over sms

Created by Daniel Frey on 03-01-2018 05:29 AM

Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file: 1. commandoversms.tcl 2. PDF with instructions on how to load and use the .tcl file.