Chapter 8: Layer 2 Switching and Spanning Tree Protocol (STP)
- Worcester Polytechnic Institute
- Electrical And Computer Engineering
- Electrical And Computer Engineering Ccna 1
- Chapter 8: Layer 2 Switching and Spanning Tree Protocol (STP)
Last Modified: 2011-07-04
What are the three switch functions?
Address learning, forward/filter decisions, and loop avoidance.
What does the "show mac address-table" do?
The "show mac address-table" shows the forward/filter table on the LAN switch.
What is the main purpose of Spanning Tree Protocol (STP) in a switched LAN?
The main purpose of STP is to prevent switching loops in a network with redundant switched paths.
What are the states of STP?
The blocking state is prevent the use of a looped path. A port in listening state prepares to forward data frames without populating the MAC address table. A port in learning state populates the MAC address table but doesn't forward data frames. A port in forwarding state sends and recieves all data frames on the bridged port. A port in the disabled state is virtually non-operational.
Be familiar with the command "showspanning-tree" and how to determine who the root bridge is.
What command will show you the forward/filter table?
show mac address-table.
If a destination MAC address is not in the forward/filter table, what will the switch do with the frame.
Flood the frame out all ports except the one it was revcieved on.
What are the three switch functions at Layer 2?
Address learning, forward/filtering, and loop avoidance.
- If a frame is received on a switch port and the source MAC address is not in the forward/filter table, what will the switch do?
- Add the source MAC address to the forward/filter table and associate it with the port the frame was received on.
What is used at layer 2 to prevent switching loops?
Spanning Tree Protocol (STP)
8022.1w is also called what?
Rapid Spanning Tree Protocol (RSTP)
When is STP considered to be converged?
When all ports are either in blocking or forwarding mode.
Switches break up ________ domains.
What is used to prevent switching loops in a network with redundant switch paths?
Which Cisco 802.1d extension stops BPDU from being transmitted out a port?
Which statement describes a spanning-tree network tat has converged?
Convergence occurs when all ports on bridges and switches have transitioned to eitehr the forwarding or blocking states. No data is forwarded until convergence is complete. Before data can be forwarded again, all devices must be updated.
- Your switch has a port status LED that is alternating between green and amber. What could this indicate?
When you connect to a switch port, at first the link lights are organge/amber, and then they turn green, indicating normal operation. If the light is blinking, you have a problem.
What commands will allow you toconfigure a Catalyst switch to be managed remotely?
- To manage a switch remotely, you must set and IP address under the management VLAN, which is, by default, interface VLAN 1. Then, from global configuration mode, you set the default gateway with the ip default-gateway command.
- Switch(configs)#ip default-gateway 192.168.10.254
- Switch(configs)#int vlan 1
- Switch(configs-if)#ip address 192.168.10.252 255.255.255.0
- Switch(configs-if)#no shut
You want to run the new 802.1w on your siwtches. Which of the following would enable this protocol?
- Switch(config)#spanning-tree mode rapid-pvst
- RSTP is not enable by default, but it is a better STP to run since it has all the fixes of 802.1d
- In which circumstance are multiple copies of the same unicast frame likely to be transmitted in a switched LAN?
In an improperly implemented redundant topology. If STP is not running on you switches and you connect them together with redundant links, you will have broadcast storms and multiple frame copies.
If you want to disable STP on a port connected to a server, which command would you use?
spanning-tree portfast - means that the port won't wait the usual 50 seconds to come up while STP is converging. (Maybe you have a server or other device connected to your network that you are sure won't create a switching loop if STP is disabled).
Layer two switching provides what?
Hardware based bridging (ASIC), Wire speed, low latency, and low cost.
- You need to allow one host to be permitted to attach dynamically to each switch interface. Which two commands must you configure on your catalyst swith to meet this policy?
- Switch(config-if)#switchport port-security maximum 1
- Switch(config-if)#switchport port-security violation shutdown
- Switchport port-security is an important command, and its super easy with CAN; however, from the CLI, you can set the maximum number of MAC addresses allowed into the port, and then set the penatly when the maximum has been exceeded.
- You have two switches connected together with two crossover cables for redundancy, and STP is disabled. Which of the following will happen between the switches?
- Broadcast storms will occur on the switch network.
- If spanning tree is disabled on a switch and you have redundant links to another switch, broadcast storms will occur, among other possible problems.
Words From Our Students
"StudyBlue is great for studying. I love the study guides, flashcards, and quizzes. So extremely helpful for all of my classes!"
Alice, Arizona State University
"I'm a student using StudyBlue, and I can 100% say that it helps me so much. Study materials for almost every subject in school are available in StudyBlue. It is so helpful for my education!"
Tim, University of Florida
"StudyBlue provides way more features than other studying apps, and thus allows me to learn very quickly! I actually feel much more comfortable taking my exams after I study with this app. It's amazing!"
Jennifer, Rutgers University
"I love flashcards but carrying around physical flashcards is cumbersome and simply outdated. StudyBlue is exactly what I was looking for!"