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Is it possible for software to detect your cable modem's MAC address or any unique factor about it?

I'm assuming you can't but I want to double check.

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Software running where? On your computer? On a server you're accessing? –  David Schwartz Jul 23 '12 at 1:40
    
Your ISP certainly can, and YOU can, as @ultra mentioned. –  JoshP Jul 23 '12 at 3:15
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4 Answers

I assume you mean if anyone can determine your cable modem's public MAC address or other identifying info?

A MAC address is only visible on the local subnet of the interface. With cable, it is might be possible to see your neighbour's MAC and IP addresses. You would need to have a means of running "tcpdump -iethx arp" on the modem's external interface. This requires special firmware. But once you have that info, what would you do with it?

As to determining a "signature" which identifies your modem by other means: That depends on your modem and how it handles various mal-formed packets, responds to various protocols, etc.. A really determined attacker can probably narrow down what brand of modem you have and then fine tune the attack.

But, are you really such a juicy target to justify that effort? ;-)

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The MAC address only exists at the Ethernet level. As soon as the connection is bridged to another protocol at the same level, information about the MAC address is lost.

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My cable modem's firmware displays an HTTP page if I navigate to 192.168.100.1. It's a Comcast provided Arris MTA (handles voice and data). First page displays all MAC addresses. Not password protected.

Hardware serial number of the cable modem is also available, as well as the serial number of the installed backup battery.

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That address (192.168.x.x) can not be directly accessed from the internet. It's called a class C private address. The MAC address can't be directly accessed through the router either. I explained a similar question to this here.

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There are no classes anymore. There haven't been since 1993, before most people ever heard of the Internet. –  Michael Hampton Jul 23 '12 at 13:57
    
Michael, Most texts STILL teach classes, and EVERY certification I'm aware of (that involves networking) asks about them. Yes, we use variable length subnetting these days. But that does NOT make my answer wrong. I've pointed this out to you before. –  Everett Apr 14 '13 at 16:34
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