Answer:
1. Firewall.
2. Router.
3. Proxy.
4. SMTP, 25.
Explanation:
1. A firewall is a network security protocol that monitors and controls inbound and outbound traffic based on set aside security rules.
Generally, a firewall is used to control access to a computer or network, as it creates a barrier between a computer or a network and the internet in order to protect against unauthorized access. It is a security system pre-installed on most computers to essentially inspect data being transmitted to or from a computer.
Furthermore, firewalls are typically bidirectional, it checks all sent and received data and only allow authorized traffic through.
2. A router can be defined as a network device that is designed typically for forwarding data packets between two or more networks based on a well-defined routing protocol.
A routing protocol can be defined as a set of defined rules or algorithms used by routers to determine the communication paths unto which data should be exchanged between the source router and destination or host device.
3. A proxy can be defined as a computer network service designed to avail end users (clients) the ability to connect indirectly to other network services. For example, a reverse proxy is a type of server that is placed right in front of other servers such as a web server and forwards or routes the user's (client) requests to those servers sitting behind it. When properly configured, reverse proxy helps to ensure security, reliability and good performance of a network.
4. A spam filter can be defined as a software program designed to process all incoming electronic messages (e-mails) and prevents any unsolicited or unwanted mail (spam) from entering the inbox of a client.
Generally, a spam filter uses SMTP with port number 25 to carry out its services.
SMTP is an acronym for Simple Mail Transfer Protocol and it uses the standard port number of 25 to provide clients with requested services.
