Ccna Icnd Chapter 2

Front 1

[201] What is a BPDU?

Back 1

[201] Bridge Protocol Data Unit - used to send Spanning Tree messages between bridges

Front 2

[202] What is STP and why is it necessary/good?

Back 2

[202] Spanning Tree Protocol. It is necessary to avoid loops when LAN segments have redundant connections.

Front 3

[203] How many states does STP use, and which are stable?

Back 3

[203] Forwarding (stable), blocking (stable), listening (transitory), learning (transitory)

Front 4

[204] What is a hello BPDU?

Back 4

[204] It is the BPDU sent every 2 seconds by the root bridge, identifying the Root Bridge's bridge ID, the cost of sending a frame to the root bridge, and the values of the timers hello Time, MaxAge, and ForwardDelay.

Front 5

[205] How is a root bridge elected?

Back 5

[205] Every bridge sends out a hello BPDU when it is first initialized, claiming to be the root bridge. The one with the lowest priority wins, if there is a tie it is decided by the one with the lowest MAC address. As switches recognize a better hello BPDU they stop advertising themselves as root and start forwarding the other hello BPDU instead.

Front 6

[206] What are root ports, and how are the selected?

Back 6

[206] Each bridge examines the hello BPDU's it receives and compares the cost of each. The interface on which it received the one with the lowest cost becomes the root port, and all other ports are blocked.

Front 7

[207] On a LAN segment, which ports are forwarded and which are blocked?

Back 7

[207] All ports on the root bridge are forwarded, all root ports are forwarded, and all designated ports are forwarded. All others are blocked.

Front 8

[208] What is a designated port?

Back 8

[208] All the bridges on a LAN segment communicate with each other and determine which of their root ports has the lowest cost to get to the root bridge - that port becomes the designated port for the LAN segment.

Front 9

[209] What are the default values for hello Time, MaxAge, and Forward Delay?

Back 9

[209] hello Time = 20 seconds; MaxAge = 15 seconds; ForwardDelay = 15 seconds

Front 10

[210] What are the default costs as set by the IEEE? (Provide original and revised)

Back 10

[210] ORIGINAL: 10 Mbps = 100, 100 Mbps = 10, 1 Gbps = 1, 10 Gbps = 1 / REVISED: 10 Mbps = 100, 100 Mbps = 19, 1 Gpbs = 4, 10 Gbps = 1

Front 11

[211] What is convergence?

Back 11

[211] Convergence is the process of reconfiguring the STP topology - it usually occurs when a link is broken.

Front 12

[212] Using STP with default settings, how long does convergence take, and why?

Back 12

[212] 50 seconds. First, a switch must wait 20 seconds to decide that its link to the root bridge has been broken. Then it flushes its MAC address table, puts its ports into listening state, and sends a TCN BPDU (Topology Change Notification) informing the other bridges to flush their tables too. After 15 seconds it puts the interfaces into learning state. After 15 more seconds it puts them into forwarding or blocking, as appropriate.

Front 13

[213] What is EtherChannel?

Back 13

[213] An optional feature that allows you to place up to 8 parallel Ethernet trunks into a group together. While normally STP would designate one the root port and block the others, using EtherChannel it considers them a single connection and forwards traffic on all ports, allowing for faster bandwidth and reducing the need for convergence - if a single link is broken the others will continue to function. The switch will only converge if all links in the EtherChannel are broken.

Front 14

[214] What is PortFast?

Back 14

[214] An optional feature that allows a switch to place a port in forwarding immediately when the port becomes active. Used when you can be sure the device connecting is not a hub or switch.

Front 15

[215] What is Cisco BPDU Guard?

Back 15

[215] If enabled, it causes the switch to disable PortFast on a port if a BPDU is received.

Front 16

[216] What is the official name of a trunk connecting two switches, as defined by Rapid Spanning Tree?

Back 16

[216] Link-type point-to-point

Front 17

[217] What is the official name of a link connecting an end-user computer to a switch, as defined by Rapid Spanning Tree?

Back 17

[217] Edge-type

Front 18

[218] What is a link-type shared connection?

Back 18

[218] A connection linking either a switch and a hub, or two hubs.

Front 19

[219] What additional port roles are defined by RSTP?

Back 19

[219] An alternate port is one on which the switch is receiving suboptimal hello BPDUs. A backup port is one located on the same LAN segment as the root port (ie, both are connected to a hub).

Front 20

[220] How does RSTP improve convergence time as compared to STP?

Back 20

[220] 1. Edge-type connections are placed immediately in forwarding (like PortFast). 2. It recognizes the loss of the root bridge in hello Time x 3 = 6 seconds. 3. Switches negotiate actively to determine the new root port and transition that port to forwarding immediately.