Member Avatar for kmk

We provide 4 port switches for students in dorm rooms. There are usually two or three students per room. Sometimes students plug in the Ethernet cables incorrectly. A couple of times this past semester, different students have looped Ethernet cables into their switch. (For example, one end is in Port 2 and the other end is in Port 3.) We have found that these students are not trying to be malicious, but they don't realize what they are doing (and sometimes are just trying to "clean up" cables that are around their room). However, when they loop a cable, it generates quite a bit of traffic on the network. In certain cases, it has bogged down and halted the Internet connection for an entire wing of student computers.

Does anyone have any suggestions on how we can prevent this problem? Is there a way to temporarily "fill in" empty switch ports? It is cost prohibitive for us to run all new cabling throughout the old dorm buildings. Any suggestions would be appreciated.

  • 3 Contributors
  • 3 Replies
  • 226 Views
  • 1 Day Discussion Span
  • Latest Post Latest Post by w1r3sp33d

Dani AI

Generated

— accidental patch-cable loops in a 4‑port room switch will generate a broadcast storm and can saturate the uplink. and started this in the right directions; below are practical, non‑intrusive steps you can apply now plus longer‑term fixes and quick troubleshooting tips.

Immediate, low‑cost steps

  • Physically block unused ports with inexpensive RJ45 port‑blockers or lockable covers so students cannot insert both ends of a cable.
  • Label the uplink clearly and secure spare cable behind the switch with a zip tie or cable tie so it cannot be easily reached.
  • Put the switch in a small locked enclosure if possible, or mount it out of easy reach.
  • Add a one‑time email/orientation note and a small decal on the switch: “Do not cross‑connect ports.”

Closet / upstream controls (managed switch required)

  • Rate‑limit broadcasts/multicast/unknown‑unicast on access ports (storm control) so a loop can’t saturate the uplink.
  • Limit MACs per access port (port‑security) to the expected number of hosts and choose a restrictive action so offending ports are contained.
  • Apply per‑port ingress policing to cap traffic from any single room.
    Example (Cisco‑style syntax — vendor CLI varies):
    
interface GigabitEthernet1/0/24
storm-control broadcast level 2.00 1.00

interface range GigabitEthernet1/0/1-4
switchport mode access
switchport port-security
switchport port-security maximum 3
switchport port-security violation restrict
switchport port-security mac-address sticky



Longer‑term and diagnostics
- If problems persist, replace the consumer 4‑port boxes with low‑cost managed edge switches that support the protections above or use a small NAT router in the room to localize problems.  
- To find the guilty room quickly: check MAC‑address table flapping and interface counters on the closet switch (use `show mac address-table`, `show interface <int> counters`, and logs). If MACs are flapping or a port’s packets jump drastically, unplug that room to restore service and then inspect its switch.

These steps combine simple physical prevention, upstream containment, and diagnostics so a single accidental cross‑plug won’t take down the wing.

Recommended Answers

All 3 Replies

Member Avatar for w1r3sp33d

what make and model of closet switches?

Member Avatar for zeroth

You could simply buy a gross of cable connectors and plug the empty connectors in the ports...

Member Avatar for w1r3sp33d

You really need to properly configure spanning tree options out at those access switches. All switches have different options, here are the features you should research to fix your problem if you run newer Cisco switches:

Portfast - puts ports automatically into forwarding, it's fast and helps with DHCP problems

UDLD - loop detection feature that shuts down a portfast switchport when a loop is detected as coming from a hub. It will require someone to "no shut" the port when it happens before it can be usable again if there is not a error disabled recovery timer set manually.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.