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2 Answers 2


A bit off topic, but I'm nominating grawity for Top Answer of the Week:

How to avoid exposing my MAC address when using IPv6?

This is what IPv6 Privacy Addressing is for. When enabled, the system will generate a temporary address with a random suffix in addition to the EUI-64-based address.

[many, many, more details]

The key is:

Grawity answered my question before I asked it. Even more: before I knew I had that question!

The full story:

I'd always assumed that I could not stop exposing my MAC address in my IPv6 addresses, as I did not find any settings for that in my router. Kudos for the commenting system, as enters grawity on one of my answers, hinting that it's not a thing of a router to start with:

Re footnote #2 - see "privacy addressing". – grawity 22 hours ago

Yup, @grawity, I noticed that extension being mentioned in RFCs, but failed to find any related settings in my consumer grade modem/router to allow for that. :-( – Arjan 22 hours ago

@Arjan: If your network is using IPv6 Autoconfiguration, then the address suffix is chosen by your own PC and this is where you should look for Privacy Addressing too. On Linux, sysctl net.ipv6.conf.eth0.use_tempaddr=1; on Windows it's netsh inter ipv6 set privacy (on by default). – grawity 20 hours ago

On a Mac: sudo sysctl -w net.inet6.ip6.use_tempaddr=1 (default value: 0). After that: ifconfig shows two IPv6 addresses; test-ipv6.com and ipv6-test.com show the temporary address. – Arjan 18 hours ago

Next, I posted this as a question, as I needed some reference when re-editing some other posts in which earlier I boldly added that IPv6 addresses often included the computer's MAC address. Given the number of favorites, I guess there were more people oblivious about having this question. :-)

  • Very nice answer, guess @kronos will have to blog twice! :P
    – Ivo Flipse
    Feb 10, 2011 at 12:51
  • 1
    Awesome question & answer!
    – Sathyajith Bhat Mod
    Feb 10, 2011 at 15:32
  • @Arjan as this is an amazing find, this will probably be the subject of next week's Question of the Week. For clarification however, why is it so necessary to hide the MAC address? The fact that the MAC address is unique solely to that computer and can be used as a backwards trace/malicious measures? Feb 10, 2011 at 15:33
  • @KronoS, because it feels like a Super Cookie. If I take my notebook on the go or change my internet provider (hence: new IPv4 address, or new IPv6 prefix), and delete all my cache, all my cookies, all Flash local shared objects, and all HTML5 local storage: my notebook might still expose that very same worldwide unique MAC address. (That said: it's more of a principle; I've not a lot to fear in the Netherlands today.) But note that the above is about the answer: grawity answering a question I didn't even ask yet. And didn't know I should ask! That's how I learn new things at Super User! :-)
    – Arjan
    Feb 10, 2011 at 15:46
  • 1
    I had no idea that IPv6 includes the mac address by default. This is a great find and very useful info for the web as a whole. Feb 10, 2011 at 16:21
  • (@Kyle, it doesn't always include the MAC, but I'm sure you've seen grawity's answer. At this time, I think Flash LSO is still a bigger thread, and soon HTML Local Storage will follow, I'm afraid...)
    – Arjan
    Feb 10, 2011 at 16:30

How do I explain how Anti-Virus protection works to a non-Super User?

I just had a client ask me this, and I really couldn't give him a good, simple, easy to understand answer. Best thing I could come up with was that each virus has a specific "fingerprint" and the software scans in known infected areas for them.

How do I explain this in a simple easy to understand fashion?

Maybe combined with:

How do anti-viruses work?

So I was thinking about viruses recently, and wondering how exactly antiviruses keep up? Considering anybody who'd been coding for a few weeks could hack together something do do nasty, nasty things to somebody's PC, the quantity alone would make a simple list of hashes prohibitive, so how do antiviruses do it? Do they monitor process activity and have a 3 strikes rule for doing virus-like things? And if so, what's stopping it from triggering on perfectly harmless things (like me moving files around in \system32)?

  • 1
    Sounds like a plan!
    – Ivo Flipse
    Feb 9, 2011 at 22:07

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