## Network A computer network is a digital telecommunications network which allows nodes to share resources. ## Client A client is a device that accesses a service made available by a server. ## Server A server is a device that provides functions or services for clients. ## Switch The primary functionality of switches is switching, which is the process of sharing resources within networks. * Have many network interfaces/ports for end hosts to connect to (usually 24+). * Provide connectivity to hosts within the same LAN (Local Area Network). * Do not provide connectivity between LANs/over the internet. * Catalyst is a Cisco switch model. ## Router The primary functionality of routers is routing, which is the process of sharing resources between networks. * ISR is a Cisco Router model. * Have fewer network interfaces than switches. * Are used to provide connectivity between LANs. ## Firewall Firewalls are specialty network security devices that control network traffic entering and exiting the network. * Network firewalls are hardware devices that filter traffic between networks. * Can be placed inside or outside the network. * Monitor and control network traffic based on configured rules. * Are known as 'Next-Generation Firewalls' when they include more modern and advanced filtering capabilities. * ASA and Firepower are some Cisco Firewall models. There is another type of firewall called 'Host-based firewall. This is a software application that filters traffic entering and exiting a host machine, like a PC. Even in a network with a hardware firewall, each host should include a host-based firewall as an extra line of defense.