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How to deny TCP traffic by IP Address on ASA 5510

Posted on 2008-10-20
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Last Modified: 2012-05-05
I'm trying to hunt down a device on my network with an IP address of 192.168.1.75, not showing up in DHCP leases. The method I want to use in finding out what it is / who it belongs to is to deny all traffic to it at the firewall level, in hopes someone will speak up.  Is there a command that can do this?
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Question by:djhath
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urgoll earned 500 total points
ID: 22760684
If you have managed switched, it might be easier to figure out its MAC address (using ping for example) once you have identified its subnet. Then query your switch to see where it hears that specific MAC address from. Once you have the port, it shouldn't be too difficult to get to the device.

That said, the way to block traffic is to create an access list and apply it to an interface. Suppose you have a firewall with two interfaces: inside and outside; support the offending device is on the inside. You could something like the snippet; it prevents the offending address from going outside (Internet, presumably), while allowing all other addresses. the acl_out prevents any incoming connections to it. There's no 'permit ip any any' on the acl_out access-list, as it would effectively open the firewall to all traffic.

IMPORTANT NOTE: do NOT copy paste the stuff below, what your access-lists should be depend on your topology, security policies and services you need to allow through.  The approach above (using managed switches) is much more preferable and doesn't depend on someone speaking up.

Good luck,
Christophe


access-list acl_in extended deny ip host 192.168.1.75 any
access-list acl_in extended permit  ip any any
access-group acl_in in interface inside
 
access-list acl_out deny ip host 192.168.1.75 any
...
access-group acl_out in interface outside

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by:djhath
ID: 22760874
Thank you for your detailed explanation.

I identified the MAC address of the offending IP by ARP cache.  Moreover, I attempted to identify the MAC address by listing the address table on my Enterasys switching stack and there are no matching ones.  It could be a wireless device, I suppose.  

I believe I'm going to attempt the ACL on the firewall.
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Expert Comment

by:lrmoore
ID: 22762169
Solarwinds Engineers toolset has a neat tool called switchport mapper. Download the free 30 day trial and run the application. It will compare the mac-address table with the arp cache of gateway router, use wins, netbios, dns lookups, use manufacturer table to tell you the brand of NIC. All of this together in a nice table for each port on the switch. It might help you.
http://www.solarwinds.com
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