Hardware

Modem – modulator / demodulator – analog phone lines – digital to analog and back

Concentrators – multiplex connected devices into one signal

Front-end processors – services I/O for main computer

Multiplexers – overlays multiple signals into one for transmission

Hub – star topology – forwards all traffic to all hosts – inefficient

Repeater – amplify signals over Distances

Layer 2:

Bridge – filter traffic between segments based on MAC address, amplify signal

Switch – forward broadcast, multipart device, forward frames based on MAC address, within networks

Layer 3:

Router – forward packets between networks based on IP address

Firewall – layer 3 & 4, up to layer 7, install between trust domains, filter by address or service

• NAT – Network Address Translation – translates private -> public IP
• PAT – Port Address Translation – uses source port number, not IP – allows to track multiple sessions
• Static packet filtering – examines packets without regard to session
• Stateful packet filtering – keeps track of session
• Proxy – hides internal network from untrusted end points