Communications Service Network

What is DHCP?

Dynamic Host Configuration Protocol (DHCP) is a method for configuring Internet Protocol (IP) network interfaces dynamically. A DHCP client does not require the user to configure an IP address, subnet mask, etc, on his computer, but rather receives these data from a DHCP server. It allows for a much easier user setup, more versitile network management, and easier support for mobile computers. DHCP is a standard protocol, defined in RFC 2131.

Do I need to register?

Any user may register his Ethernet card's hardware or "MAC" address with the DHCP server. (The term "MAC address" is from the Media Access Control protocol of Ethernet, and has nothing to do with the Apple Macintosh.) This registration is required for anyone who would like to use roaming DHCP (public portal) access. It is important to note that CNS does not provide the portals for public access, but rather works with the sponsoring department to manage the IP address assignment method.

To register your Ethernet card for roaming access log in to the MAC address registration web page with your PID and password.

Note that the registration process associates your PID to your device, so if you change or add devices you will have to change your registration. This can also be done on the MAC address registration web page. There is no mechanism for a non-Virginia Tech affiliate to register for DHCP.

Residence Hall Reserved IP address assignment

There is no support for static IP assignments in the residence halls.

What about hostnames?

If you receive a dynamic IP address, the DNS server will have an arbitrary domain name associated with your address. This will allow you to use servers that require domain names, and for most users this is all that is needed.

How do I see what IP address, etc, I have?

To see what IP address, etc, you recieved from the DHCP server:

  • Windows: From the Command Prompt, ipconfig
  • Mac: Network Preference panel, or from the Terminal, ifconfig
  • Unix: varies. ifconfig <interface> or ifconfig -a almost always works, but there are some dhcp commands that are platform-specifc for more DHCP-specific info.

The router or gateway should always be the ".1" host in your subnet (e.g., if your address is, your gateway should be If it isn't, there may be a serious security problem, and you should call 4-Help or 1-6780 immediately.

What if I have problems?

If you encounter problems configuring your computer to use DHCP, or have general questions, call 4-HELP (or 231-HELP). If you know that your computer is configured properly and are having difficulty getting a response from a DHCP server, call the Network Operations Center at 231-6780.

Communications Network Services
1770 Forecast Drive (0506)
Blacksburg, Virginia 24060
(540) 231-6460
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