(Incomplete) Chapter 2 - Basic Switching Concepts and Configuration

Question 1

How does a Cisco switch boot?

Answer 1

• POST
• Boot loader
• CPU initialization
• Load flash
• Load iOS
• Hands control to iOS.

Question 2

What are the modes of the System LED?

Answer 2

• Off: System is off
• Green: System is operating normally
• Amber: System is receiving power, but not functioning properly

Question 3

What are the modes of the Redundant Power System (RPS) LED?

Answer 3

• Off: RPS is off or not properly connected
• Green: Connected and ready
• Green blinking: Connected, but providing power to another device.
• Amber: Standby mode or in a fault condition
• Amber blinking: Internal power supply has failed. RPS is providing power.

Question 4

What are the modes of the Port Status LED?

Answer 4

• Off: No link
• Green: Default mode. Link present
• Green blinking: Activity. Port is sending or receiving data
• Green/amber: Link fault
• Amber: blocked to prevent loops.

Question 5

What are the modes of the Port Duplex LED?

Answer 5

• Off: Half duplex

- Green: Full duplex

Question 6

What are the modes of the Port Speed LED?

Answer 6

• Off: 10 Mbit/s
• Green: 100 Mbit/s
• Blinking green: 1000 Mbit/s

Question 7

What are the modes of the Power over Ethernet LED (PoE)?

Answer 7

• Off: Ports are denied power or placed in fault condition
• Blinking amber: At least one port has been denied power or in fault condition
• Green: PoE is selected. The ports will blink in different colors
  - Off: PoE is off
  - Green: PoE is on
  - Green/amber: Denied, because it will exceed
  switch power capacity
  - Blinking amber: Off, due to fault
  - Amber: PoE is disabled on the port

Question 8

What is the difference between half- and full duplex?

Answer 8

• Half duplex: Only one direction for data flow

- Full duplex: Data flows in both directions (100% efficiency)

Question 9

What is auto-MDIX?

Answer 9

A feature, in which the router or switch is able to detect the connection type (crossover or straight-through).

Question 10

What are the different modes, when checking for interface status?

Answer 10

Interface and Line protocol status:

• Up/Up: Operational
• Down/Down: Interface problem
• Up/Down: Could be encapsulation mismatch or a hardware problem. The interface could also be error disabled.

Question 11

What is a Runt frame?

Answer 11

A frame that is shorter than the minimum 64 byte requirement.

Question 12

What is a Giant frame?

Answer 12

A frame longer than the maximum 1548 byte limit.

Question 13

What are some common causes for a CRC error?

Answer 13

It is usually a media or cable error. Most common errors are:

• Electrical interference
• Damaged connection
• Incorrect cable type
• Length (not as common)

Question 14

What are some of the characteristics for collisions?

Answer 14

• Expect collisions in half duplex (completely normal)

- There should be no collision errors in full duplex mode

Question 15

What is a late collision?

Answer 15

A late collision can occur after the first 512 bytes of the frame has been transmitted.

• Most common cause is cable length
• Can also occur because of duplex miss-configuration

Question 16

How do you verify SSH support?

Answer 16

S1# show ip ssh

Question 17

How do you configure SSH on a switch?

Answer 17

Switch (config)# hostname S1
S1 (config)# enable secret 0 cisco
S1 (config)# ip domain name cisco.com
S1 (config)# crypto key generate rsa (1024 bits is recommended as a minimum)
S1 (config)# username admin secret cisco
S1 (config)# line vty 0 15
S1 (config-line)# transport input ssh
S1 (config-line)# login local
S1 (config-line)# exit

Question 18

What is MAC address flooding?

Answer 18

An attack where the attacker overwhelms the switch, by sending frames with fake MAC addresses. The switch forwards the frame to every port, if the MAC address is unknown.

Question 19

How does a DHCP starvation attack work?

Answer 19

An attacker floods the DHCP server with requests, thereby using up all available IP addresses.

Question 20

What is DHCP spoofing?

Answer 20

An attack where the attacker sets up their own DHCP server, issuing IP addresses to clients. The main focus for this attack is to make the clients use a false DNS or WINS server, making the the attacker’s server act as default gateway. DHCP snooping can be used to prevent this.

Question 21

What is Cisco Discovery Protocol (CDP)?

Answer 21

A proprietary protocol that all Cisco devices can use to identify neighbor devices. Most routers and switches have this enabled by default.

Contains information about:

• IP addresses
• iOS software version
• Platform
• Capabilities
• Native VLAN

Can be disabled by running:
S1 (config)# no cdp run