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Data Link Addresses
Addresses that operate at the data link layer. A MAC address is a data link layer address and these are
built in by the manufacturer and cannot usually be changed. They can be virtualized for Adapter Fault
Tolerance or HSRP. Switches and Bridges operate at the Data Link layer and use Data Link addresses
to switch/bridge.
Network Addresses
Addresses that operate at the Network Layer. These are IP addresses or IPX addresses that are used by
Routers to route packets. Network addresses are made up of two parts, the Network number and the
Host ID. IP addresses are 32 bit dotted decimal numbers. IPX addresses are 80 bit dotted hexadecimal
numbers. Network addresses are host specific and one must be bound to each interface for every proto-
col loaded on the machine. There is no fixed relationship between the host and the Network Address.
For example, a router with three interfaces, each running IPX, TCP/IP, and AppleTalk, must have three
network layer addresses for each interface. The router therefore has nine network layer addresses.
*Keypoints:MAC addresses uniquely identify devices on the same medium.MAC addresses consist of 48 bit hexadecimal numbers.Know what a valid MAC address looks like.IP addresses are 32 bit dotted decimal numbers.MAC addresses are copied into RAM when the network card initializes.A Network address consists of 2 parts 1) Network number and 2) Host number.The hardware address is used to transmit a frame from one interface to another.Why a Layered Model?
Standardizing hardware and software to follow the 7 layers of the OSI Model has several major bene-
fits:
1) It reduces complexity
2) Allows for standardization of interfaces
3) Facilitates modular engineering
4) Ensures interoperability
5) Accelerates evolution
6) Simplifies teaching and learning
Data Encapsulation
Data encapsulation is the process in which the information in a protocol is wrapped, or contained, in
the data section of another protocol. In the OSI model each layer encapsulates the layer immediately
above it as the data flows down the protocol stack. The encapsulation process can be broken down into
5 steps.
At a transmitting device, the data encapsulation method is as follows:
ActionOSI ModelKeyword
1 Alphanumeric input of user is converted to data.
Application/Presentation/Session
DATA
2 Data is converted to segments.
Transport
SEGMENTS
3 Segments are converted to Packets or Datagrams
and network header information is added.
Network
PACKETS
4 Packets or Datagrams are built into Frames.
Data Link
FRAMES
5 Frames are converted to 1s and 0s (bits) for
transmission.
Physical
BITS