Other than the explanation below How can switches help reduce network security problems?
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Switches can be used to disallow access to a network by requiring authentication to the server to all computers that plug in to a network LAN connection requiring each computer to authenticate itself. This workgroup switch is called an authenticator. This process occurs by the transmission of the password against the authentication database. If the password is verified, then the confirmation is sent back to the workgroup switch and access is granted. Additionally, when an employee is let go it is simple to quickly revoke the access of the individual on the switch. It is important that access rights to a network, allowing only authorized users access, is easily managed.
Additionally, switches are used to secure the network from other systems that could pose a threat to the network resources. They can detect and respond to threats such as virus’ and attacks on the network. Switches allow their administrators to set detection and response security policies.
Ethernet switches can be used to create virtual LANs (VLANs). VLANs create logically separate LANs on the same physical switch. Each port of the switch is assigned to a VLAN. They are used for security purposes, keeping personnel on one VLAN from being able to reach servers on another VLAN. Though SANS recommends that VLANs not be used for enforcing security policy.