2009 February

IP Addresses and Security

A reader wrote me to ask about IP address security. I’m not really sure whether he meant keeping his IP address a secret, or whether he was asking if someone could break into his network and use his ISP connection with his IP address, so, let’s first look at the idea of keeping one’s IP address a secret…

Terry,I just recently came across your site and have joined your online email newletter. I have a question relating to I.P.addresses.I have a home network,router(encrypted /password required ),a firewall (not Win xp),several antispyware programs.The other day my ISP sent me an email,alleging I had violated copyright laws and had downloaded a movie from some place in [identifying information removed - Terry].I called my ISP and we discussed it,I did not download any movies and never heard of the film co.in question,my concern was how would they obtain my IP address,as it is like a fingerprint.I asked my ISP is there any way a 3rd.party could gain access to my wireless network and they could not provide an answer as to how this happened and advised me to disregard it.Is there a way for a 3rd.party to obtain my IP address ?? this is a security concern to myself and my wife. Thank you for your time

I wrote back to him to explain thatt the real question is not how they got his IP address, but how they tied that IP address to him. Only his ISP can do that, unless you logged in somewhere (or used an ID that linked to his name or email address) or in the program used to access it.

First, let’s go through how TCP/IP works – how the computers communicate like …

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Home Networking — Wired + Wireless Connections

The simplest way to set up a home network, including both computers with wired connections and computers with wireless connections, is to set up a wireless router immediately following your DSL modem or Cable modem. Sometimes, a DSL modem even has the router built into it.

In this setup, all the computers are assigned their IP addresses by the DHCP server that is built into the router. All are on the same logical network. However, their ability to share files, printers, and otherwise communicate between each other will depend on your settings in each computer.

In order to share files, you have to tell Windows (or Linux, etc.) to enable file and printer sharing, identify which directories should be shared, and have the computers on the same Windows Workgroup (or Windows domain, if you’re a very advanced user running a Windows domain controller). You’ll also have to tell the firewall programs on each computer to allow the sharing with the other computers — or the firewall will block the data.

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