Ethernet Fundamentals Flashcards
Ethernet Fundamentals Overview
Please refer to study guide for info/diagrams
CSMA/CD
Carrier Sense Multiple Access/Collision Detect
Carrier Sense: Listen to the wire, verify it’s not busy
Multiple Access: All devices have access at any time
Collision Detect: If two devices transmit at same time, a collision occurs.
Back off, wait random time, try again
Collision Domains
Comprised of all devices on a shared Ethernet segment (same cable or hub)
Devices operate at half-duplex when connected to a hub
Collision Domains with Switches
Ethernet switches increase scalability of the network by creating multiple collision domains.
Each port on a switch is a collision domain (no chance of collisions), increases speed
Hub
Layer 1 device “Multiport repeaters”
Passive Hub: Repeats signal (no amplification)
Active Hub: Repeats signal with amplification
Smart Hub: Active hub with enhanced features (SNMP)
Bridges
Analyze source MAC address in frames entering the bridge & populate an internal MAC address table.
Make intelligent forwarding decisions based on destination MAC address in the frames.
Switch
Layer 2 device (Connects multiple network segments)
Essentially a multiport bridge
Learn MAC addresses & make forwarding decisions based on them.
Analyze source MAC in frames entering the switch & populate internal MAC table based on them.
Router
Layer 3 device (Connects multiple networks together)
Makes forwarding decisions based on IP addresses
More feature-rich & support broader range of interface types than multilayer switches
Each port is a separate collision/broadcast domain.
Layer 3 Switch
Layer 3 device (Connects multiple network segments)
Can make layer 3 routing decisions & interconnect entire networks (like a router)
Link Aggregation
802.3ad
Congestion can occur when ports all operate at same speed
Allows for combo of multiple physical connections into a single logical connection
Bandwidth available is increased & congestion minimized/prevented.
PoE
Power Over Ethernet (802.3af)
Supplies electrical power over Ethernet
Requires CAT5+
Up to 15.4 watts of power to device
PoE+ (802.3at)
Up to 25.5 watts of power to device
Device Types:
PSE (Power Sourcing Equipment)
PD (Powered Device)
Port Monitoring/Mirroring
Helpful to analyze packet flow over network
Network sniffers can see all traffic on a hub
Switches require port monitoring to see all traffic
Port mirroring makes a copy of all traffic destined for a port & sends it to another port
User Authentication
802.1x
For security purposes, switches can require users to authenticate themselves before gaining network access
Once authenticated, a key is generated & shared between the supplicant and the switch/authenticator
Auth server checks supplicant’s credentials & creates the key
Key is used to encrypt the traffic to/from the client
Management Access & Authentication
SSH: Remote admin program that allows you to connect to the switch over the network
Console Port: Allows for local admin of the switch using a separate laptop & a rollover cable (DB-9 to RJ-45)
OOB
Out-of-Band Management:
Involves keeping all network config devices on a separate network
First-Hop Redundancy
HSRP (Hot Standby Router Protocol) uses a virtual IP & MAC to provide an “active” & “standby” router
Cisco proprietary protocol
If active is offline, standby answers
Other First-Hop Redundancy Protocols
GLBP (Gateway Load Balancing Protocol)
Cisco proprietary protocol
VRRP (Virtual Router Redundancy Protocol)
Open-source
CARP (Common Address Redundancy Protocol)
Open-source
STP (Protocol)
Spanning Tree Protocol (802.1D)
Permits redundant links between switches & prevents looping of network traffic
SPB (Shortest Path Bridging) is used for larger network environments