Responsible for moving messages from one node to another until they reach the destination
host
Principal protocol is
IP (Internet Protocol)
o
Adds its own Network layer message to the segment or datagram, and the entire
Network Layer message is now called a
packet
o
IP Address –
an address assigned to each node on a network, which the Network Layer
uses to uniquely identify each host
o
Relies on several routing protocols to find the best route for a packet to take to reach
destination
ICMP (Internet Control Message Protocol) and ARP (Address Resolution
Protocol)
o
If 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 Layer
Layers 2 and 1 are responsible for interfacing with physical hardware on the local network
o
Protocols at these layers are programmed into firmware of a computer’s NIC and other
hardware
Type of networking hardware or technology used on a network determine the Link Layer
Protocol used
o
Ethernet and Wi-Fi are examples
Puts control information in a Link Layer header and at the end of the packet in a
trailer
Entire Link Layer is called a
frame
o
The frame header contains the hardware addresses of the source and destination NICs.
This is called the
MAC (Media Access Control)
address.
o
The physical addresses are short-range addresses that can only find nodes on the local
network
Layer 1: Physical Layer
Simplest layer and is responsible for sending bits via a wired or wireless transmission
Can be transmitted as:
o
Wavelengths in the air (Wi-Fi)
o
Voltage on a copper wire (Ethernet on a twister-pair cabling)
o
Light (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 next
o
Technicians loosely call this group of bits a message or transmission
Removing a header and a trailer form a lower layer’s PDU is called
decapsulation
Safety Procedures and Policies
Fire Suppression System
o
Emergency 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 other
means
o
Portable fire extinguishers
o
Emergency power-off switch
o
Suppression agents – consist of a foaming chemical, gas, or water that sprays
everywhere to put out the fire
Fail Open or Fail Close
o
Does the security system allow access during a failure (fail open) or deny access during
the failure (fail close)?
o
Example: 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)
o
Example: 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
