01 - Network Models Flashcards
Protocols
sets of rules, regulations, standards, and procedures that enable hardware and software developers to make devices and applications that function properly at a particular layer
OSI Seven Layers
Layer 7 - Application Layer 6 - Presentation Layer 5 - Session Layer 4 - Transport Layer 3 - Network Layer 2 - Data Link Layer 1 - Physical
Layer 1
Physical Layer
- anything that moves data from one system to another (copper cabling, fiber optics, radio waves)
NIC
Network Interface Card
- interface between PC and network
MAC Address
- Media Access Control Address
- special firmware burned onto ROM chip
- 48-bit identifier
- no two NICs share the same MAC address
- first 6 digits - OUI - Organizationally Unique Identifier
- last 6 digits - Device ID
View MAC address in Windows CLI
ipconfig /all
View MAC address in Linux CLI
ip a
View MAC address in Mac CLI
ifconfig
Other names for MAC Address
- MAC-48
- EUI-48 (Extended Unique Indentifier)
Frame
a container for a chunk of data moving across a network
Unit of data at each layer is called?
PDU (Protocol Data Unit)
PDU for Layer 2
Frame
Different frame types
Different frame types are used on different networks, however, all NICs on the same network must use the same frame type
Parts of a Frame
Header:
- Receiving MAC Address
- Sending MAC Address
- type field - indicates whats encapsulated in the frame
Payload:
- data
Trailer:
- FCS
Frame Size
1500 bytes
FCS
Frame Check Sequence
- 4 bytes long
- contains CRC
- tells recieving NIC if frame was received in good order
Layer 2 Broadcast Address
FF-FF-FF-FF-FF-FF (6 sets)
Unicast Address
Any frame addressed specifically to another device
What is Layer 2
Data Link Layer
- any device that deals with MAC addresses
Two jobs of a NIC
LLC
- Logical Link Control
- aspect of the NIC that talks to the OS via device drivers
Media Access Control
- creates and addresses Frames
Physical vs Logical Addressing
Physical - MAC addresses
Logical - IP Addresses
Network Protocol
uses logical addressing instead of physical addressing
TCP/IP
Transmission Control Protocol / Internet Protocol
What is Layer 3
Network Layer
- addresses packets to go from one network to another
Layer 3 PDU
Packets
How to routers route?
IP Addresses
Chopping data up to send out on a network
Segmentation and Reassembly
Transport Protocol data chunks
Segments (TCP/IP) - get sequence numbers
Datagrams (UDP) - no sequence
What is Layer 4
Transport Layer
- segmentation/reassembly
- also requests packets that weren’t received in good order
What is Layer 5
Session Layer
- initiates, accepts, opens and closes sessions
- connects applications to applications
View sessions windows CLI
netstat -a
What is Layer 6?
Presentation Layer
- translates data from lower layers into a format usable by the application layer, and vice versa
What is Layer 7?
Application Layer
- code built into all OSs that enable network aware applications
- done through APIs (Application Programming Interfaces)
