The name lets suggest the following functionality:
– Access point: provides a connection for wireless devices to the LAN
– Routing: realizes the routing between the LAN subnets and between LAN and WAN
But most of them do actual way more than just that:
– Switch: provides multiple connection ports for wired devices to the LAN
– DHCP-Server: automatically assigns IP addresses to the LAN components
– DNS-Server: resolves domain names to IP address (if unknown, forward to ISP)
– Gateway: is an exit/entry point for the communication between LAN and WAN
– NAT: translates all private IP’s (LAN) to a public IP (WAN) and vice versa
– Modem: de-/modulates the signals for the traffic between LAN and WAN
– Firewall: allows traffic from the WAN only if it was initiated from the LAN