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
Broadcast Storms
If broadcast frame received by both switches, they can forward frame to each other
Multiple copies of frame are forwarded, replicated, & forwarded again until the network is consumed with forwarding many copies of the same initial frame
Root Bridge
Switch elected to act as a reference point for a spanning tree
Switch with lowest bridge ID (BID) is elected as root bridge.
BID is made up of a priority value & MAC (lowest value considered the root)
Nonroot Bridge
All other switches in an STP topology
Root Port
Every non-root bridge has a single root port
Port closest to the root bridge in terms of cost
If costs are equal, lowest port number is chosen
Designated Port
Every network segment has a designated port
Port closest to the root bridge in terms of cost
All ports on root bridge are designated ports
Non-Designated Port
Ports that block traffic to create loop-free topology
