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In my university, I needed to register the MAC address of my personal laptop with the admin in order to use the university network. Now, it seems like I am assigned a unique network address "lastname.university.com", as my login prompt shows:

Last login: Wed Aug 16 07:45:38 2017 from lastname.university.com

Is it a problem (e.g. security or privacy) that this address contains my last name? Is it exposed to the outside world, e.g. when I am browsing the web?

  • 4
    @AbraCadaver: Actually X-Forwarded-Host contains the host that the client requested (ie it's usually the name of the website you're visiting, not the computer making the request). The client details may be in X-Forwarded-For, but that contains IP addresses rather than hostnames. If the IP address is not private, and if the lastname.university hostname is exposed in the public DNS, then the name may be exposed. – psmears Aug 17 '17 at 11:39
  • @psmears: Just looked it up, you're right I had my wires twisted. – AbraCadaver Aug 17 '17 at 12:34
  • It is quite possible what they are using is the name of your machine not the name of you. In that case you can probably change it to anything you want, for example by editing /etc/hostname and rebooting. – kasperd Aug 17 '17 at 20:16
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    Presumably university.com is mit.edu, because nobody else has enough IPv4s to hand them out like candy... – R.. Aug 18 '17 at 2:49
  • @kasperd: No, they are using my name, and not the name of my computer. – traindriver Aug 18 '17 at 8:41
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Whether this is visible to the outside world depends on what kind of firewall your university network uses.

You could try using the tools at www.whatismyip.com to see some of what's being exposed to the public Internet. The basic info at the home page will show you what public IP you have; you can compare this with the configuration of your PC to see if they're the same (the PC may have a private IP, and the public IP is is the address of the university's firewall).

If your internal IP is being exposed, the university may still be using split DNS to provide different name resolution internally and publicly. Use the Reverse DNS Lookup tool to see what name is being exposed to the public. I expect it will be a generic name derived automatically from the IP, not the one with your name in it.

Also, it's possible that the university uses dynamic address assignment that doesn't associate a specific IP with your PC permanently. Each time you connect to the network you may get a different IP. So if some outside site has your IP saved, and tries to look up the name later, they may get someone else's name because the assignment has changed. The "Last login" message you see in the login greeting on your server isn't affected by this because it saves the name when you login, not the IP.

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    Thanks for these links. As feared, what my IP says about me reveals: Host Name: lastname.university.com – traindriver Aug 17 '17 at 7:24
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    You could try asking the network helpdesk if there's a way to hide your name. You're probably not the only student concerned about privacy. – Barmar Aug 17 '17 at 7:31
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    This is exactly what I am doing. – traindriver Aug 17 '17 at 7:42
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What's your IP address? If it's an RFC 1918 address like 10.*, then you're being NATted to the Internet, and as a comorbid condition* your reverse DNS won't be visible to external sites. It will still allow the University to track you better internally, which is perhaps why they do it.

If it's not an RFC 1918 address, your DNS name likely does show up externally; you can check with a site like WhatIsMyIP (Reverse DNS Lookup).


*Having an RFC 1918 address implies that your reverse DNS won't be publicized on the Internet, because an RFC 1918 address must be translated (NAT, or Network Address Translation) before going out to the Internet. In almost all cases, NAT is one-to-many (one public address, many private addresses) or pool-to-many (some public addresses, many private addresses) so there is no one-to-one mapping between the internal RFC 1918 address and the external address the Internet sees traffic from. If you have hundreds or thousands of students being NATted to one or more public IP addresses, having that smaller number of public IP addresses be mapped to hundreds or thousands of names becomes meaningless. All of which I glibly summarized as "NAT means no external reverse DNS" above.

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    I think your answer is correct, but what would be the security/privacy consequences of either option? – lucidbrot Aug 16 '17 at 18:09
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    If it's not an RFC 1918 address, your DNS name likely does show up externally - Why? You can split horizon reverse DNS zones just as easily as you do it for forward zones. – Zoredache Aug 16 '17 at 23:19
  • @Zoredache simply because RFC 1918 implies one-to-many or pool-to-many NAT, either of which would make publicizing reverse data relatively useless. While it is possible to have one-to-one NAT, and to use split DNS to publish name mappings both inside and outside, in practice that's a highly improbable setup... I'll update the answer to clarify this. – gowenfawr Aug 16 '17 at 23:41
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    I think @Zoredache's question was more about the opposite situation: if it's not an RFC1918 address, then you can't assume the name will show up externally - it's easy enough to set up DNS so that internal and external IP-to-hostname lookups get different answers. – psmears Aug 17 '17 at 11:42
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Your hostname may be included in the Received headers added to any emails sent from that host (and not passing through NAT to the first MTA to handle them). You can find out if that's currently happening by sending a test email to an 'echo' reflector, but that doesn't tell you what server changes may affect that in the future.

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No it is not really a security or privacy issue. It just seems to be an internal DNS name assigned to you on your university network. Networks usually have split DNS i.e. internal and external. If your network is properly setup with NAT, internal host names do not resolve from outside.

  • it turns out in this case that it was public, and there was a PTR record with his name. – fabspro Aug 17 '17 at 9:56
-1

If you really want your name to remain private, you'll need a lot more than hiding the DNS entry of your computer. Most universities will give you an e-mails formed from your first / last name, and many also have a public directory of their staff. Make a request to have a non-default e-mail address and be excluded from any directories and address books. For the latter, you're usually given an agreement to sign when you start working, and you usually can opt-out.

Needless to say, if you're planning to participate in research, make sure you pick a pseudonym for your publications, otherwise your name will become irrevocably public and tied to the university. And even if you use a pseudonym, that won't completely hide your identity, since you will still need to use your real name in many places which may be publicly visible, like conference participant lists or grant applications.

  • -1: this doesn't answer my question at all. – traindriver Aug 18 '17 at 8:40

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