All switch ports will rarely be used simultaneously on devices in a network. Such a situation should always be avoided because it will make the network unscalable and impossible for future upgrades. A more realistic scenario is when a single set of interfaces is used on a device while the rest are idle.
As much as it does not sound like unused ports could cause any harm, it is quite easy for someone to take advantage of those open ports and threaten the network. Therefore, it is important to secure unused ports on a Cisco switch.
Unused ports on a switch can be an entry point for unauthorized access to the network. Attackers can connect to them and gain access to the network, which can result in data theft, network disruption, and other security threats.
They can also be used to connect rogue devices to the network. Rogue devices are not authorized to be on the network and can cause security breaches by stealing data, spreading malware, and engaging in other malicious activities.
Finally, unused ports can be a target for denial of service (DoS) attacks, where an attacker floods the network with traffic, causing the switch to run out of resources and impacting network performance.
To mitigate these risks on a Cisco switch, it is important to secure the unused ports by performing three simple but very important steps:
- Shutdown: First, disable any unused ports. If you don’t need them, there is no point in having them enabled. This allows free access to any devices connecting to them.
- Access mode: Configure all those unused ports on the switch in access mode, which does not allow a trunk to be created, but only an access link. As a result, the interface can belong to only one VLAN instead of exchanging data for all available VLANs on the switch.
- VLAN access: To increase security, you can assign the same ports to an unused VLAN, so any potential connection to them would provide access to a place (VLAN) where nothing happens, or in other words, access to a black hole.
Configuration Example to Secure Unused Ports
The process of securing unused ports consists of only a few steps. The following example configuration provides the necessary steps that should be applied to several unused ports on a switch:
In addition to disabling the ports, you should configure them to operate in access mode, assign them to a black hole VLAN, and disable the VLAN. The configuration example below shows how to create or enter a black hole VLAN and shut it down. When you shut down a VLAN, all traffic on that VLAN stops.
