LAN Switching Technologies

Question 1

What is the root bridge

Answer 1

The perceived centre of the network

Has lowest bridge id

Question 2

How does STP find the best path in a network

Answer 2

Elect root bridge
Find best path to the root bridge
Block what is left over

Question 3

How is the best path to the root bridge determined

Answer 3

Lowest cost
lowest bridge ID
Lowest port ID

Question 4

How is the root bridge elected

Answer 4

Lowest bridge priority
Lowest bridge mac
Combined = bridge ID

Question 5

What is portfast

Answer 5

Disables STP

Means it won’t spend the usual 50 seconds to come up while STP is converging

Question 6

What is bpduguard

Answer 6

Security feature

Disables interface when receiving bpdu

Question 7

What are the STP modes

Answer 7

• Common spanning tree (CST or STP – 802.1d)
• Per VLAN Spanning Tree (PVST+)
• Rapid Spanning Tree (RSTP – 802.1w)
• Per-VLAN Rapid Spanning Tree (PVRST)
• Multiple Spanning Tree Protocol (MSTP – 802.1s)

Question 8

What are the 3 types of port modes in STP

Answer 8

Designated
Forward
Block

Question 9

What are the STP link costs of each cable type

Answer 9

• 10 Mbps – 100
• 100 mbps – 19
• 1 gbps – 4
• 10 gbps – 2

Question 10

STP priorites can be set in intervals of…

Answer 10

4096

Question 11

802.1X is also known as..

Answer 11

EAP (extensible authentication protocol)

Question 12

What is DHCP snooping

Answer 12

Stops rogue DHCP attacks by using trusted ports

All ports are untrusted by default

Question 13

What is the native vlan

Answer 13

Untagged vlan, by default vlan 1

Question 14

What are the two etherchannel protocols

Answer 14

PAgP

LACP

Question 15

What are the features of PAgP

Answer 15

Cisco proprietary

Modes: on, desirable, auto

Question 16

What are the features of LACP

Answer 16

Industry standard

Modes: on, active, passive