Switching Flashcards
Main role of LAN switch
Forward Ethernet frames using logic:
1. Decides to forward or filter frame via Dest. MAC
2, Learning MAC address via Source MAC
3. Creating loop free environment via STP
4. Supports full-duplex, doubling its bandwidth available to the device
Bridge
A prelude to the switch; separates collision domains
If a frame enters the switch and no source MAC is in the table….
The switch creates an entry in its MAC address table
Inactivity timer
Timer for each MAC address entry in the MAC address table of switch; resets back to 0 if it receives frame from same MAC address
No destination MAC entry in table…
Switch floods unknown unicast, multicast, and broadcast frames to all ports except the incoming port
Store-and-forward processing
switch receives the entire frame before forwarding the first bit of the frame
cut-through processing
starts sending the frame out the outport asap; propogates errors b/c FCS is in the Ethernet trailer
fragment-free processing
receives the first 64 bytes of the frame before forwarding it, reducing errors
Full-duplex
allows devices to transmit and receive at the same time, doubling bandwidth
LAN switching summary
- Each port provides dedicated bandwidth to a single device
- Allows multiple simultaneous conversations b/n devices on different ports
- Supports rate adaptation (different Ethernet speeds supported)
Switches are in ________ of the OSI model
Layer 2
If frame is a known unicast address, but outgoing interface is the same is incoming interface….
switch will filter frame, meaning that the switch simply ignores the frame and doesn’t forward it
Hubs allow…..
a collision domain to spread from one side of the device to another
Only device that can separate broadcast domains are..
Routers
Collision domain
a set of NICs for which a frame sent by one NIC could result in a collision with a frame sent by any other NIC in the same collision domain
A LAN consists of….
all devices that are on the same broadcast domain
Campus LAN
created to support multiple buildings that are in close proximity to each other
Access switches
Switches connected directly to end users, providing user access to the LAN
Distribution switches
provide a path through which the access switches can forward traffic to each other
Core switches
forward traffic between distribution switches
Autonegotiation*
each node picks the best options that both nodes support: the fastest speed and the best duplex setting
10-BASE-T
CAT3 or better, two pair, 100m
100-BASE-T
Fast Ethernet; CAT5 UTP or better; two pair; 100 m
1000BASE-T
Gigabit Ethernet; CAT5e UTP or better, four pair; 100 m
1000BASE-SX
Multimode fiber; 550 m
1000BASE-LX
Multimode fiber; 550 m; 50- and 62.5-micron fiber
1000BASE-LX
9-micron single-mode fiber (laser); 5 km
IEEE autonegotiation rules
Use slowest speed
If speed is 10, 100 use half duplex; otherwise use full duplex
Hub autonegotiation
uses the IEEE rules for choosing default settings, which often results in devices using 10 Mbps and half-duplex
The switch CLI can be accessed by three methods…
Telnet, SSH, or the console
Console requires…
A connection betweent the serial port of PC and the switch’s console port; rollover cable is needed
A difference b/n Telnet and SSH
Telnet sends all data as clear-text data while SSH encrypts this
Switches can support up to __ simultaneous Telnet sessions
16
SSH requires ____ for login
username and password
Debug command
Asks the switch to continue monitoring different processes in the switch.
Configuration commands
Are commands that tell the switch the details of what to do and how to do it; changes switch configuration immediately
Useful debug commands
no debug all
undebug all
debug
RAM memory
Used for working storage (active configuration)
ROM memory
stores bootstrap program that finds the full Cisco IOS image and manages the process of loading Cisco IOS into RAM
Flash memory
Stores Cisco IOS images and default location where the switch gets its Cisco IOS at boot time
NVRAM
stores the initial or startup configuration file
reload command
erases RAM and copies start config into RAM
erase startup-config or erase nvram
erases startup-configuration file
terminal monitor (hint: debug)
EXEC (enable) command that sends a copy of all syslog messages, including debug messages, to the Telnet or SSH user who issues this command
