What is Port Security?

Port Security is a network security mechanism on switches that controls which devices can connect to a specific physical port.

In simple terms: Port Security decides which devices are "allowed" on each switch port.

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#Why Port Security is needed

Without Port Security:

• any device can be connected to a free port;
• an attacker can gain access to the internal network;
• attacks from the local network become possible.

Port Security allows you to:

• limit the number of devices on a port;
• allow connections only from known MAC addresses;
• prevent unauthorized access.

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#How Port Security works

The switch checks the MAC addresses of devices connecting to a port and applies rules:

• if the MAC address is allowed, access is granted;
• if it is not allowed, the port is blocked or the traffic is dropped.

It is usually used at the access layer.

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#Main features of Port Security

#1. Limiting the number of MAC addresses

For example:

• only 1 device can be connected to a port;
• if a second one appears, protection is triggered.

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#2. Recording allowed MAC addresses

MAC addresses can be:

• static (set manually);
• dynamic (learned automatically);
• sticky (learned and saved).

Sticky MAC is the most popular option.

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#3. Reaction to a violation (violation mode)

If the rules are violated, the port can:

• Protect, which simply blocks the traffic;
• Restrict, which blocks it and logs the event;
• Shutdown, which fully disables the port (the strictest option).

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#Which attacks Port Security prevents

• connecting someone else's laptop to the network;
• MAC flooding;
• unauthorized access to the local network.

This is protection at the data link layer (L2).

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#Limitations of Port Security

It is important to understand:

• a MAC address can be spoofed;
• it does not protect against attacks above L2;
• it requires administration.

That is why Port Security is part of a multi-layered defense, not the only security measure.

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#A simple example

Port Security is like:

an outlet with an access list: power is supplied only to the devices that are on the list.