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Responsible for moving messages from one node to another until they reach the destination hostPrincipal protocol is IP (Internet Protocol)oAdds its own Network layer message to the segment or datagram, and the entire Network Layer message is now called a packetoIP Address – an address assigned to each node on a network, which the Network Layer uses to uniquely identify each hostoRelies on several routing protocols to find the best route for a packet to take to reach destinationICMP (Internet Control Message Protocol) and ARP (Address Resolution Protocol) oIf the Network Layer Protocol is aware that a packet is larger than the maximum size for its network, it will divide the packet into smaller packets in a process called fragmentation
Layer 2: Data Link LayerLayers 2 and 1 are responsible for interfacing with physical hardware on the local networkoProtocols at these layers are programmed into firmware of a computer’s NIC and other hardwareType of networking hardware or technology used on a network determine the Link Layer Protocol usedoEthernet and Wi-Fi are examplesPuts control information in a Link Layer header and at the end of the packet in a trailerEntire Link Layer is called a frameoThe frame header contains the hardware addresses of the source and destination NICs. This is called the MAC (Media Access Control) address.oThe physical addresses are short-range addresses that can only find nodes on the local network Layer 1: Physical LayerSimplest layer and is responsible for sending bits via a wired or wireless transmissionCan be transmitted as:oWavelengths in the air (Wi-Fi)oVoltage on a copper wire (Ethernet on a twister-pair cabling)oLight (fiber-optic cabling)Protocol Data Unit (PDU)The technical name for a group of bits as it moves from one layer to the next and from one LAN to the nextoTechnicians loosely call this group of bits a message or transmission
Removing a header and a trailer form a lower layer’s PDU is called decapsulationSafety Procedures and PoliciesFire Suppression SystemoEmergency Alert System – generate loud noise and flashing lights. Some send text and voice messages to key personnel, and post alerts by email, network messages, and othermeansoPortable fire extinguishersoEmergency power-off switchoSuppression agents – consist of a foaming chemical, gas, or water that sprays everywhere to put out the fireFail Open or Fail CloseoDoes the security system allow access during a failure (fail open) or deny access during the failure (fail close)?oExample: during a fire alert, using a fail-open policy, all exit doors stay unlocked so that people can safely leave the building and firefighters can enter the building, even though it poses a security risk for thieves entering the building (fail open)oExample: if firewall software protecting access to a database of customer credit card numbers fail, it might be configured to fail close and to deny access to the database until