Ethernet Basics Flashcards
Five Fields of Ethernet Frames
1) Destination Address (MAC)
2) Source Address (MAC)
3) Data Type
4) Data itself
5) Frame Check Sequence (FCS)
Preamble
Appears in front of the frame, notifies receiver that new data is coming
7 bytes followed by 1 byte “start frame delimeter”
MAC Address size
48 bits (6 bytes)
Pad
Minimum frame size is 64 bytes
If not enough data to reach minimum, padding data added
FCS
Frame Check Sequence
Like hashing - sending computer runs data against a cyclic redundancy check and attaches the results (FCS)
Receiving system does the same CRC, should be able to match their FCS
Cyclical Redundancy Check
CRC - math calc done against a frame’s data to generate an FCS
Receiving system does same check to confirm data is not corrupted
Ethernet Network Naming Convention
(e.g. 10BASE-T)
10 - speed (10 Mbps)
BASE - signaling type (Baseband means one signal at a time, vs broadband)
T - cabling type (twisted pair)
10BASE-T Standard
Cat 3 cable
Pins 1, 2 for send data, pins 3, 6 to receive data
Max distance to hub: 100m
Max Computers: 1024/hub
half-duplex
a NIC that can only send/receive asynchronously
full-duplex
a NIC that can send/receive at the same time
TIA/EIA 568A
1 - GW
2 - G
3- OW
4 - Blue
5 - BW
6 - O
7 - BrW
8 - Br
TIA/EIA 568B
1 - OW
2 - O
3- GW
4 - Blue
5 - BW
6 - G
7 - BrW
8 - Br
10BASE-FL Specs
Speed: 10Mbps
Signal: Baseband
Distance: 2000m
Max Computers: 1024/hub
Topology: star-bus, physical star, logical bus
Cable Type: Multimode 62.5/125 micrometers, ST or SC connections
Media Converter
Allows translation of signal between cable types (fiber and copper)
CSMA/CD
Carrier-sense multiple access with collision detection
Carrier-sense multiple access with collision detection
CSMA/CD
Carrier-sense: each node using network checks cable before sending data frame to see if busy
Multiple access: al machines have equal access to wire (first come, first served)
collision detection: NICS register if a collision occurs, each generates a random number to retry
Media Access Control address table
Internal cache of all the MACs attached to a switch, created during port mapping
Uplink Port
Connection between two switches via straight-through cable
straight-through cable
A cable connected to the uplink port of one switch and to a regular port of another
Modern switches do not have dedicated uplink ports but auto-detect a straight-through cable
auto-medium-dependent interface crossover
MDI-X
Auto sensing of straight-through cable
crossover cable
one end is 568A, the other 568B
Means switch 1 sends through transmit pair, but signal lands on switch 2’s receiving pair
Not necessary anymore with modern switches with MDI-X)
STP
Spanning Tree Protocol
eliminate accidental switching loops
Spanning Tree Protocol
STP
typically enabled by default
Uses special frames for switches to communicate to each other
Bridge Protocol Data Units (2 types)
BPDUs
the special STP frames
1) Configuration BPDU
2) TCN BPDU
