Ethernet Basics Flashcards
Ethernet
networking technology based on bus topology
topology of every Ethernet since 90’s
hybrid star-bus
[blank] prevent monopolization of shared cable
frames
Ethernet traffic management
each computer listens on segment
sends frame when no other transmission are detected
basic Ethernet frame
1 - MAC address of frame's recipient 2 - MAC address of sending system 3 - type of data 4 - data 5 - pad (if needed) 6 - FCS
preamble
7-byte series of binary followed by a 1-byte start frame
allows NIC to realize frame is coming & know where it starts
added by sending NIC
MAC address (bit & byte)
48-bit
6-byte
pad
minimum frame size - 64 bytes
fills remaining space when content does not reach 64 bytes
CSMA/CD
carrier sense multiple access/collision detection
determines which computer should use shared wire at a given moment
carrier sense
each node examines cable before sending frame
traffic detected - wait a few milliseconds - recheck
multiple access
all machines have equal access to the wire if cable is free
1st-come, 1st-served
collision
nodes transmit signal simultaneously
both signals are lost
hub sends overlapping signals - NICs immediately detect collision - stop transmitting
maximum acceptable collisions
10%
collision domain
group of nodes that have the capability of sending frames at the same time as each other
Ethernet collision domains are [blank]
segments or connected segments
bus Ethernet
thicknet - 10Base5 - vampire tap
thinnet - 10Base2 - T connector attached to NIC
thinnet specifics
RG-58 coax
BNC connects on ends
185 m limit
half-duplex vs. full-duplex
half - communicate in 1 direction at a time
full - send/receive simultaneously
TIA/EIA
Telecommunications Industry Association / Electronics Industries Alliance
current TIA/EIA standard
568C
same wiring standards as A & B
new name “ANSI/TIA-586-C”
TIA/EIA 568A
1 - G / W 2- G 3 - O / W 4 - Bl 5 - Bl / W 6 - O 7 - Br / W 8 - Br
G - send | O - receive
TIA/EIA 568B
1 - O / W 2 - O 3 - G / W 4 - Bl 5 - Bl / W 6 - G 7 - Br / W 8 - Br
O - send | G - receive
sending pins
1 & 2
receiving ping
3 & 6
10BaseT
- Speed = 10 Mbps
- Signal Type = baseband
- Distance = 100 meters between hub and node
- Node Limit = No more than 1024
- Topology = star-bus, physical star, logical bus
- Cable Type = CAT 3 or better UTP cabling with RJ-45 connectors
10BaseFL
- Speed = 10 Mbps
- Signal Type = baseband
- Distance = 2000 meters between hub and node
- Node Limit = no more than 1024
- Topology = star-bus, physical star, logical bus
- Cable Type = multimode fiber-optic cabling with ST or SC connectors
[blank] used to interconnect different types of Ethernet
media converter
couplers
extend Ethernet segments
double-female connectors
add machines not originally envisioned
adding more ports for additional nodes
add more hubs
add a bridge
2 methods of connecting hubs
uplink port > straight through cable from uplink port on 1 hub to any other port on the other hub
crossover cable > send/receive pairs are reversed to create operational connection - connects to regular port
configuration for connecting multiple hubs
must use daisy chain > uplink port connects to 1 port on each attached hub
different names for uplink ports
crossover > MDI-X > MDI > OUT
line (marking) on hub between 2 ports may indicate [blank]
only 1 of these 2 ports may be used at a time
MDI
media dependent interface
regular port on hub or switch
MDIX or MDI-X
media dependent interface crossover
uplink port
ends of crossover cable
1 end TIA/EIA 568A
1 end TIA/EIA 568B
rollover cable
RJ-45 connector on 1 end > RS-232 serial port on the other
used to connect computer directly to Cisco switch or router
straight-through cable connecting 2 PCs directly
both PCs will try to use the same send/receive wires
plug 2 PCs into a hub
hub electronically crosses data wires
1 NIC sends > the other receives
plug 2nd hub into 1st hub using regular ports
cross the cross
create a straight-through connection
bridge
acts like a repeater or hub to connect 2 Ethernet networks
filters & forwards traffic between segments based on MAC address
preserves bandwidth
*layer 2 - work with MAC addresses”
filter
stop traffic from crossing from 1 network to the next
forward
pass traffic from 1 side of the bridge to the other
10BaseT network with a hub can support [blank] signals on the wire at a time
1
switch
effectively creates point-to-point connection between 2 computers on a network
allows for full access to the network bandwidth
essentially eliminate collisions
SAT
source address table
table of MAC addresses generated by a switch
SAT creation
switch starts off just like a hub > forwards incoming signals to all other ports
frames forwarded > switch copies MAC addresses
quickly creates table of MACs for each connected computer
how switches allow access to full network bandwidth
each port on switch is its own collision domain
switch can buffer incoming frames
half- vs. full-duplex switches
half-duplex have to follow CSMA/CD
full-duplex do not > don’t have to daisy chain
Layer 2 switches
switch filters
run on MAC addresses
unicast message
only sent to recipient MAC address
broadcast message
sent to all connected ports
domains of switch vs. hub networks
switch - broadcast domain
hub - collision domain
Ethernet before switches
no difference between broadcast & collision domain
all messages were broadcast - went to all nodes
all nodes connected to the same bus
collisions were normal
bridging loops (switching loops)
switches can be connected in any fashion
redundant connections (loops) may be created
crashed early switch networks
STP
Spanning Tree Protocol
enabled switches can detect loops > communicate with other switches > set looped port’s state to blocking
BPDU
Bridge Protocol Data Unit
type of frame used by switches to communicate with each other to determine things like distance between them & changes to the network
STP-enabled switch receives frame from MAC address not contained in SAT
switch sends out a signal on every port to determine location of new device
flooding
all switches exchange information > update tables > set ports to forwarding or blocking
convergence
bridge loops with modern switches
STP enabled on all modern switches
bridge loop designed intentionally to provide fault tolerance
link fails > blocking port becomes forwarding port to maintain traffic flow
portfast
always forward traffic
RTSP
Rapid Spanning Tree Protocol
significantly faster convergence time
6 seconds compared to 50 seconds
switch troubleshooting
connected device can’t access network
look for obvious changes
link lights > try a different port
check all connections & cables
replace cable or switch with 1 that is known to work
