The difference between an open and closed network is the authentication and security in place. The same hardware and software can be used for either network; it is more of a design for use rather than a topology.
An open network, also known as a public network, is one that is accessible to anyone. On an open network, the internet is accessible, and the network has the ability to connect to other networks.
There are security concerns associated with a public network such as packet sniffing, inadvertently sharing information with other computers on the network, and malware. To avoid some of the issues, users should turn off sharing, use a virtual private network (VPN) when possible, enable a firewall, and use encrypted communications such as HTTPS and TLS.
Some operating systems like Windows provide default security configurations, depending on the type of network selected. For example, the operating system security configuration will be more relaxed when selecting “home” network versus “public” network. A home network is assumed to have fewer threats than a public network with unlimited unknown users.
In a closed network, in addition to authenticating and authorizing users, the network requires the devices also to be authenticated and authorized. Data and communications that are sent and received within a closed network do not have any external connectivity to the extranet. Outside parties and or devices are prohibited from accessing closed networks, as they are considered potentially malicious and untrustworthy.
A closed network can also refer to a wireless local area network (WLAN), where users and devices must be aware of the name or the service set identifier (SSID) to connect to wireless access points within the network if the WLAN is not sending out its name in beacon frames.
Devices that do not have the SSID of the WLAN and preauthorization to access will have no access to the closed network. Constructed properly, closed networks can be effective in mitigating potential external and internal malicious users and devices.