LAN Switching

Question 1

What causes the risk of a layer 2 loop forming in a switch topography

Answer 1

A frame unlike a packet does not have a TTL field in the packet or Time To Live field, so it could loop around in the topography forever

Question 2

What happens if the same Mac address comes into another port of a switch

Answer 2

The Mac address table will be updated such that the Mac address will now be listed under the other port

Question 3

How is a root switch elected in a topography

Answer 3

The switch with the lowest bridge id (and Mac address if there needs to be a tiebreaker) is elected to be the root switch

Question 4

What are the four spanning tree protocol port states

Answer 4

Root port - non root switch port closest to root switch (lower interface on root switch if there needs to be a tie breaker), Designated port - one for each segment, port closer to root switch, rest are blocked ports

Question 5

The higher the speed of the link in a network topography running spanning tree,

Answer 5

the lower the cost of the link

Question 6

What’s the traditional convergence time of STP and how is it broken down

Answer 6

Total 50 seconds, 20 seconds blocking and waiting for BPDU, Listening State: 15 seconds, Learning State: 15 Seconds

Question 7

What is BPDU

Answer 7

Bridge Protocol Data Unit

Question 8

What is the difference between PVST and PVST+

Answer 8

PVST (Per VLAN Spanning Tree) is used over ISL trunks while PVST+ is used over IEEE 802.1Q trunks

Question 9

What is RSTP

Answer 9

Rapid PVST+ fast convergence, one instance for each VLAN

Question 10

What are the three port states of PVST+

Answer 10

Discarding, Learning, Forwarding (No Listening State Here)

Question 11

What’s different about rapid STP

Answer 11

sends a BPDU to all neighbors instead of TCN TCA and then TC BPDU

Question 12

What is VLAN Trunking Protocol

Answer 12

You set a new VLAN in one of the center VLANS and the switch sends VTP advertisements out of their trunk ports, allowing each switch down the way to learn that there’s a new VLAN

Question 13

What is a client mode for a switch

Answer 13

The switch is updated with VLAN information advertisements, but cannot modify or change it, can originate and forwards VTP messages

Question 14

What is server mode for a switch

Answer 14

The switch can change VLANs and any changes are propogated across the network

Question 15

What is transparent mode for a switch

Answer 15

You can make changes to the local database but the changes are not advertised over the trunk ports and does not update its database from advertisements, no orign of VTP advertisements but receives VTP messages and forwards them

Question 16

What is an alternate port in RPVST

Answer 16

Alternate way to get to root bridge

Question 17

What is a backup port in RPVST

Answer 17

When there’s a redundant link on a shared segment (such as two connections to a hub)

Question 18

What is port fast

Answer 18

Port fast, under the condition that the port connects to an endpoint on the network, activates immediately. With port fast, the Listening and Learning stages are skipped; available only on non-trunking ports (so no switch to switch)

Question 19

What is BPDU guard

Answer 19

In whatever case when one connects a switch to a supposed portfast connection, BPDU guard will transition to block any BPDU sent out and put the port down into err disable mode to prevent a topological loop