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Protocol Definitions List

DHCP Servers

Dynamic Host Configuration Protocol (DHCP) service is available for all computers on our campus network. This service provides a variety of functionality and is required for some computers to work properly. To register a computer or device, please visit the Connecting to the Network page.

Running your own DHCP service for any reason anywhere on our network is prohibited. If a rogue DHCP server is located, the computer will be removed from the network, and (if registered) its owner contacted.

A rogue DHCP server may hand out incorrect information to booting machines, and any machine that listens to this rogue DHCP server's offers will not function correctly. As this will cause those with properly configured computers to lose all network connectivity, running a DHCP server of your own is banned. To be sure that you do NOT accidentally turn on this service when installing the operating system:

Windows XP: Do NOT enable Internet Connection Sharing (i.e., Network Bridging) while connected to the campus network. Also, do NOT install the Microsoft DHCP Server or DHCP Relay Agent network services.
Mac OS X
: Do NOT enable Internet Connection Sharing while connected to the campus network.
Linux / UNIX
: Do NOT install DHCP server packages. Most distributions include a DHCP client, which you are encouraged to use.

IP Routing

Some operating systems offer the ability to act as a router and forward IP packets from one network interface to another based on its internal routing tables. No computers on campus should have a need to do this. Because of this, IP Routing is banned.

If a computer is configured to route IP packets from one interface to another and both are on the same physical network, the packets will appear on the wire twice. As a result, ARP caches may become corrupt because two possible interfaces have received packets for one host.

When hosts are incorrectly configured as routers, information is disseminated incorrectly. In order to advertise which networks are available on other interfaces, the host must send route advertisements in one format or another. These advertisements may impair the real routers from receiving information or may cause them to advertise the incorrect routes. To be sure that you do NOT configure your operating system for IP routing:

Windows XP: Do NOT enable Internet Connection Sharing (Network Bridging).
Mac OS X: Do NOT enable Internet Connection Sharing while connected to the campus network.

Virtual Hosting via Multiple IP Addresses

Individuals may have a network host that will serve WWW data for multiple virtual sites. These sites may have different hostnames (, that are short and easy to remember. Carnegie Mellon does not provide multiple IP addresses to hosts. If this functionality is needed, the host may be setup with multiple valid hostnames.

To establish a host with multiple valid hostnames, consider these tips:

  • The host may have two separate hostnames, and the web server is smart enough to determine which hostname was used, or the host may have two separate hostnames which point to two separate IP addresses, which the web server uses to determine what the request was for.
  • Linux users should not configure "Networking options: Network aliasing: IP: aliasing support." Aliasing support is not permitted on the campus network.

Last Reviewed: 11/4/11