DHCP Snooping and Dynamic ARP Inspection

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Sep 28th, 2009
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In order to reduce the impact of ARP spoofing attacks, I would like implement DHCP snooping and dynamic Arp inspection feature features on our Cisco enterprise network.

Test were conclusive for all devices connected directly to cisco switches.

However, I still have problems with devices connected to SOHO unmanaged switches.

Could you indicate me please, how I can overcome this problem.

You can find in attachment an example diagram.

Printer1 and PC2 cause connectivity problem when port Fa0/23 on switch S2 is configured as untrusted.

When I configure that port as trusted, I still can operate successfull ARP spoofing attacks with Cain & Abel software.

Best Regards,


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Giuseppe Larosa Mon, 09/28/2009 - 02:12
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Hello Mustapha,

indeed DHCP snooping and DAI would fit with a design where no unmanaged switches are present so that a one-to-one corrispondence between MAC addresses of PCs and printers and ports can be done.

in your case you could just use port security with DHCP snooping trusted state as a way to mitigate at least MAC flood attacks.

Hope to help



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