Open Systems Interconnect Model (OSI) Introduction

Router shown as a circle - Thunderbolt is a serial connection

====== Layer One  - Physical ======
 
Cables

Repeaters

Hubs repeats the signal to all other ports except the port that originated the signal

Base - Baseband - one at a time
Broadband - More than one signal at a time

====== Layer Two - Data Link ======

- controls data on the immediate physical link between devices

MAC Media Access Control 48 bits hexidecimal

OUI Field 24 bits is vendor specific

7th most significant bit - UL - if turned off (0) - the address should be universally unique
-- The 7th bit turned on (1) - the address has been assigned locally

Protocal unit called a frame
FCS - Frame Check Sequence aka CRC - cyclic redundancy check

Switches work here

Switches learn MAC addresses by looking at the source address field in the frame
Switches make their forwarding decisions based on the destination MAC address in the frame
Once the MAC tabe

Flood is not the same as a broadcast, flood is done when 
broadcast has all FF in the destination MAC address in the frame
broadcast is a one to all transmission sent on purpose
unicast is a one to one sent message


Cisco packet tracer  CLI -> show mac address-table

DYNAMIC -> switch learned port 

bia - burned in address

Layer 2 - Broadcast Domains

switch = transparent bridging

Broadcast - all switches are one broadcast domain by default
Broadcast - can not transverse a router

Collision domains - 
----

**Encapsulation** = layer header + data

4- Transport Layer chunk of data = Segment - 

3- Network Layer - chunk of data - packet

2- Data Link Layer - chunk of data - frame 
- Ethernet - MAC address

1- Physical Layer


**Data Networks and Addressing**

Addressing at the Data Link Layer - frame 

media access control - 48 bit hexadecimal number local address MAC - 

1st 24 bits = manufacturer ID 

2ne 24 bits = serial number

Packet Internet or Inter-Network Groper (PING) used to test the reachability of a host on an Internet Protocol (IP) network. 



**Cisco Certifications**

  * Entry Level - CCENT - Entry Network Technician
  * Associate - CCNA - Network Associate - most common - Route/Switch
  * Professional - CCNP - Network Professional
  * Expert - CCIE - Internetworking Expert