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Old 06-16-2002, 09:14 PM   #1
Registered: Jan 2002
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Mac Addresses

Is there a way with iptables to retrieve someone mac address when they are snooping around or trying ot get into your machine? I know Black Ice does it but is there a way of doing this in Linux?
Old 06-17-2002, 12:16 AM   #2
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I'm not sure how you'd get iptables to automatically log MAC addresses, but you can display your current ARP cache by typing "arp -a".

Old 06-20-2002, 06:08 AM   #3
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Not from a remote network.
IP protocol doesn't use or carry MAC addresses outside of your local network.

Old 06-22-2002, 10:16 AM   #4
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ip carries different hardware addresses from router to router
Old 06-22-2002, 11:54 PM   #5
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IP Tables can't do the job, but wouldn't a packet sniffing tool such as Snort or Ethereal yield the source MAC address?
Old 06-23-2002, 12:23 AM   #6
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snort and ethereal would work if it was a local network, but not remotely.

Old 07-01-2002, 10:55 PM   #7
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Let me set the story right. IP has nothing to do with MAC address. All IP knows is dumb old 32-bit IP address. MAC address (at least for traditional LAN's) are handled by Ethernet.

Let me describe this better. I'm going to give you a little OSI theory.

OSI Model

Layer 7 -- Application Layer
Layer 6 -- Presentation Layer
Layer 5 -- Session Layer
Layer 4 -- Transport Layer
Layer 3 -- Network Layer
Layer 2 -- Data Link Layer
Layer 1 -- Physical Layer

I'm only going to deal with Layer 2

Layer 2 is the Data Link Layer, its the lowest connection to the wire (i.e. Cat-5 or telephone line, etc.) Its also the last layer of encapsulation before data is transmitted in its binary electrical form. It's also the Layer where Ethernet exists. Ethernet is where the notorious MAC address lives. An Ethernet frame contains both Sending and Receiving MAC addresses of devices on LAN. Notice I said LAN. Ethernet exists independents of IP and later TCP. All Ethernet does is tack on what it knows about where its going and wheres it's being sent from. (MAC addresses of sending and receiving hosts)

Now when network communication leaves your network or a few hops after that. Ethernet Frames get stripped off and sent further using more high level encapsulation such as HDLC on Serial Links. So when the Ethernet is stripped the MAC's get lost! So as I see it The MAC address you get on your LAN from the Internet are that of either your ISP or maybe even your own router.

Whew I know that wasn't clear.


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