This is a post especially for those of you who live on Emerson’s Boston campus. No, it is not about Saint Patrick’s Day, HempFest, or the Red Sox. It’s about DHCP. Some on-campus-dwelling, Boston-based Emersonians experienced an interruption in wired network service on Monday, March 10th. This happened because a rogue (read: unauthorized) DHCP server was intercepting traffic on our network and preventing users from connecting to the internet.
DHC-whaaaaa? DHCP: Dynamic Host Configuration Protocol. DHCP is what computers use to join a network, and to obtain the information they need in order to connect to the internet. It is a protocol, a system of rules by which computers communicate with one another. It’s not a language, but a conversation.
What’s being said?
- If it’s the first time your computer has ever been plugged in to a network, it broadcasts a discover message.
- DHCP servers connected to the network see this message and recognize that a device is looking for information. They respond with an offer, which includes important information needed to join a network: an IP address (so you can send and receive packets), the domain’s nameservers (so you can type google.com into your address bar instead of 18.104.22.168), the time servers (so your computer knows what time it is), and more.
- The computer then requests to use the IP address and other information included in the DHCP server’s response.
- Finally, the DHCP server can either acknowledge or deny this request. If the request is acknowledged, the computer is connected to the internet! If the request is denied, the whole conversation starts over again.
Any DHCP server plugged in to a network can start offering IP addresses to requesting clients. There are lots of devices that can function as DHCP servers. This Apple AirPort Extreme, for example. If someone plugs the WAN port on one of these babies into our student wired network, it starts behaving like a DHCP server right alongside our own. What it doesn’t have is any of the correct information: it provides computers with invalid IP addresses, blank nameserver IPs, etcetera, which make it impossible for the computer to connect to the internet. So it’s handing out BS to students’ computers and stopping them from gaining access to the internet. This is what we experienced on Monday.
The networking team located the rogue device in a dorm room, disabled the ports it was connected to, and forwarded the necessary information to Housing and Residence Life so they could contact the student and take action. Now is a good time to remind everyone using Emerson’s network, wired or wireless, of our Electronic Information Policy. Item three in the list of Guidelines for Ethical Behavior reads:
Network services and wiring may not be extended beyond the port provided. Retransmission or propagation of network services is prohibited without explicit permission. This includes the installation of hubs, switches and wireless equipment.
Please remember that any unauthorized networking equipment you bring to your dorm room, in addition to violating policies you agreed to abide by, impacts the quality of service we can provide you and students living around you. If you are experiencing issues with connectivity or wireless signal strength, contact the Help Desk at (617) 824-8080 or put in a ticket at it.emerson.edu/help.