Modules 1-4 Flashcards
1
Q
Which command will display a summary of all IPv6 -enabled interfaces on a router that includes the IPv6 address and the operational status.
A
show ipv6 interface brief
2
Q
When verifying routes, what code is used to identify directly connected routes in the routing table?
A
C
3
Q
Which command will display packet flow counts, collisions, and buffer failures on an interface?
A
show interface
4
Q
What character is used to enable the filtering of commands?
A
Pipe |
5
Q
Which filtering expression will show all output lines starting from the line matching the filtering expression?
A
begin
6
Q
Which tasks can be accomplished by using the command history feature?
A
Recall previously entered commands.
Set the command history buffer size.
7
Q
A network administator has configured VLAN 99 as the management VLAN and has configured it with an IP address and subnet mask. The administator issues the show interface vlan 99 command and notices that the line protocol is down. Which action can change the state of the line protocol to up?
A
Connect a host to an interface associated with VLAN 99.
8
Q
Which statement best descrives SVIs?
A
A default SVI is created for VLAN 1 for switch administration.
9
Q
Which prompt is displayed when a network administrator successfully accesses the boot loader on a switch to recover from a system crash?
A
Switch:
10
Q
What must an administator have in order to reset a lost password on a router?
A
Physical access to the router.
11
Q
When configuring a switch for SSH access, what other command that is associated with the login local command is required to be entered on the switch?
A
Username [username] secret [secret]
12
Q
Which two special characteristics do LAN switches use to alleviate network congestion?
A
Fast port speeds.
Fast internal switching.
13
Q
Which characteristic helps alleviate network congestion when a 10 Gbps port is forwarding data to a 1 Gbps port?
A
Frame buffering
14
Q
Which switching method makes use of the FCS value?
A
Store-and-forward
15
Q
Which two statements are true about half-duplex and full-duplex communications?
A
Full duplex allows both ends to transmit and receive simultaneously.
Full duplex increases the effective bandwidth
16
Q
Which option correctly describes a switching method?
A
Store-and-forward: ensures that the frame is free of physical and data-link errors.
17
Q
What is the purpose of frame buffers on a switch?
A
They hold traffic, thus alleviating network congestion.
18
Q
Which network device can be used to eliminate collisions on an ethernet network?
A
Switch
19
Q
True or false? It is best practice to configure the native VLAN as VLAN 1.
A
False.
20
Q
True or false? DTP is an open standard IEEE protocol that specifes auto negotiation of switch trunk links.
A
False
21
Q
What is the default switchport mode for Cisco Catalyst switches?
A
Dynamic Auto
22
Q
True or False? Two switchports on a link both configured as dynamic auto will successfully negotiate a truck.
A
False
23
Q
Which two DTP modes will form a trunk with an interface that is configured as dynamic auto? (There are two)
A
Trunk
Dynamic desirable
24
Q
In which memory location are the VLAN configurations of normal range VLANs stored on a Catalyst switch?
A
Flash
25
What is the purpose of the vlan.dat file on a switch?
It holds the VLAN database.
26
A network administrator is determining the best placement of VLAN trunk links. Which two types of point-to-point connections utilize VLAN trunking? (Pick two)
Between a switch and a server that has an 802.1Q NIC.
| Between two switches that utilize multiple VLANs.
27
What are three primary benefits of using VLANs (choose three.)
IT Staff efficiency
Security
Cost reduction
28
On a Cisco switch, where is extended range VLAN information stored?
Running configuration file
29
In which location are the normal range VLANs stored on a Cisco switch by default?
Flash
30
For what reason would a network admin use the show interfaces trunk command on a switch?
To view the native VLAN.
31
Where is the vlan.dat file stored on a switch?
In Flash memory
32
A Cisco switch currently allows traffic tagged with VLANs 10 and 20 across trunk port Fa0/5. What is the effect of issuing a switchport trunk allowed vlan 30 command on Fa0/5?
It allows only VLAN 30 on Fa0/5.
33
You are troubleshooting an inter-VLAN on a switch and need to verify that the subinterfaces are in the routing table. Which inter-VLAN routing troubleshooting command would you use to do this?
show IP route
34
You are troubleshooting an inter-VLAN issue on a switch and need to check the list of VLANs and their assigned ports. Which inter-VLAN routing troubleshooting command would you use to do this?
Show vlan
35
You are troubleshooting an inter-VLAN issue on a router and need to verify the status of an access port and its access mode VLAN. Which troubleshooting command would you use to do this?
Show interfaces [interface-id] switchport
36
You are troubleshooting an inter-VLAN issue on a router and need to verify the status and IP address of all interfaces in a condensed format. Which inter-VLAN routing troubleshooting command would you use to do this?
Show ip interface brief
37
A PC is to access a web server on another network. Which inter-VLAN method will provide the highest bandwidth at Layer 3 and also provide a default gateway for the PC?
Muiltilayer switch with routing enabled.
38
Which scalable method must be implemented in order to provide inter-VLAN routing on a switched network with more than 1000 VLANs?
Routing traffic internally to a Layer 3 switch device.
39
When configuring a router as a part of a router-on-a-stick inter VLAN routing topology, where should the IP address be assigned?
To the subinterface
40
Which type of inter-VLAN communication design requires the configuration of multiple subinterfaces?
Router-on-a-stick
41
While configuring inter-VLAN routing on a multilayer switch, a network admin issues the no switchport command on an interface that is connected to another switch. What is the purpose of this command?
To create a routed port for single network
42
A network administrator enters the following command sequence on a Cisco 3560 switch. What is the purpose of these commands?
Switch(config)# interface gigabitethernet 0/1
Switch(config-if)# no switchport
To make the Gi0/1 port a routed port
43
What operational mode should be used on a switch port to connect it to a router for router-on-a-stick inter-VLAN routing?
Trunk
44
Which sentence correctly describes the SVI inter-VLAN routing method?
An SVI is needed for each VLAN.
45
How is traffic routed between multiple VLANs on a multilayer switch?
Traffic is routed via internal VLAN interfaces.
46
What is required to perform router-on-a-stick inter VLAN routing?
A router that is configured with multiple subinterfaces.
47
An administrator was troubleshooting a router-on-a-stick topology and concluded that the problem was related to the configuration of VLANs on the router subinterfaces. Which two commands can the admin use in the router to identify the problem?
Show ip interface
| Show running-config
48
Which statement describes STP?
STP is a Layer 2 loop prevention protocol for Ethernet LANs.
49
Without STP on the Ethernet LAN, which three types of frames could cause a catastrophic loop in the network? Choose three.
Unknown unicast.
Multicast
Broadcast
50
What device is elected by the Spanning Tree Algorithm? All other switches determine a single least-cost path to this device.
Root bridge
51
By default (without any configuration on a switch), what will determine which switch is the root bridge?
The MAC address of the switch.
52
The root bridge will be the switch with the:
Lowest bridge ID
53
The port closest to the root bridge in terms of least overall cost (best path) to the root bridge is the:
Root port
54
The port on the segment (with two switches) that has the lowest path cost to the root bridge is the:
Designated port
55
Which of the following ports will forward Ethernet frames?
Designated port.
| Root port.
56
The sum of individual port costs along the path from the switch to the root bridge is known as the:
Root path cost.
57
How often does a switch send a BPDU?
Every 2 seconds.
58
Which three STP port states are merged into the RSTP discarding port state? (Choose three)
Disabled
Blocking
Listening
59
Which protocol was designed to bring faster convergence to STP?
RSTP
60
Which technology solves the problem of a device being unable to get an IPv4 address from a DHCP server due to STP forwarding delay timers?
PortFast
61
Which port state will switch ports immediately transition to when configured for PortFast?
Forwarding
62
After the election of the root bridge has been completed, how will switches find the best paths to the root bridge?
Each switch will analyze the sum of all port costs to reach the root and use the path with the lowest cost.
63
Which is the default STP operation mode on Cisco Catalyst switches?
PVST+
64
During the implementation of STP, all switches are rebooted by the network admin. What is the first step of spanning-tree elections process?
All the switches send out BDPUs advertsing themselves as the root bridge.
65
Which two concepts relate to a switch that is intended to have only end devices attached and intended never to be used to connect to another switch? Choose two.
PortFast
| edge port
66
Which three port states are used by Rapid PVST+?
Discarding
Learning
Forwarding
67
When PVST is running over a switched network, which port state can participate in BPDU frame forwarding based on BPDUs received, but does not forward frames?
Listening
68
Which STP port role is adopted by a switch port if there is no other port with a lower cost to the root bridge?
Root port
69
Which two statements describe a switch port that is configured with PortFast? Choose two.
The switch port immediately transitions from blocking to the forwarding state.
The switch port should never receive BPDUs.
70
What additional info is contained in the 12-bit extended system ID of BPDU?
VLAN ID
71
An admin is troubleshooting a switch and wants to verify if it is a root bridge. What command can be used to do this?
show spanning-tree
72
Which are benefits of EtherChannel technology?
Fault-tolerance
Load sharing
Increased bandwidth
Link redundancy
73
Which three are PAgP interface modes? Choose three.
On
Auto
Desirable
74
Which combinations of PAgP modes will form an EtherChannel
Auto>desirable
| on>on
75
An EtherChannel link using LACP was formed between two switches, S1 and S2. While verifying the configuration, which mode combination could be utilized on both switches?
S1-passive and S2-active
76
When a range of ports is being configured for EtherChannel, which mode will configure PAgP so that it initiates the EtherChannel negotiation?
Desirable
77
Which three interface parameters must match for an EtherChannel to form?
Trunking mode
Allowed VLANs
Native VLAN
78
What are three advantages of using EtherChannel technology? Choose three.
There is no need to upgrade links to faster connections to increase bandwidth.
A spanning tree recalculation is not required when a single link within the channel goes down.
Configuration tasks can be done on the EtherChannel interface.
79
When EtherChannel is implemented, multiple physical interfaces are bundled into which type of logical connection?
port channel
80
When a range of ports is being configured for EtherChannel by the use of PAgP, which mode will form the bundled channel only if the port receives PAgP packets from another device?
Auto
81
Which statement is true about EtherChannel technology?
EtherChannel uses existing switch ports.
82
Which two mode combinations would result in the successful negotiation of an EtherChannel. Choose two.
Active: passive
Desirable: desirable
83
Which two protocols are link aggregation protocols? Choose two.
802.3ad
| PAgP
84
When a range of ports is being configured for EtherChannel, which mode will configure LACP so that it initiates the EtherChannel negotiation?
Active
85
What will happen if a network admin puts a port that is part of an EtherChannel bundle into a different VLAN than the other ports in that bundle?
The EtherChannel will fail.
86
When a range of ports is being configured for EtherChannel, which mode will configure LACP on a port only if the port receives LACP packets from another device?
Passive.
87
Describe the 5 steps in the switch boot sequence (very similar for routers too). What command can be used to specify which system image (IOS) a switch should load?
Step 1: First, the switch loads a power-on self-test (POST) program stored in ROM. POST checks the CPU subsystem. It tests the CPU, DRAM, and the portion of the flash device that makes up the flash file system.
Step 2: Next, the switch loads the boot loader software. The boot loader is a small program stored in ROM that is run immediately after POST successfully completes.
Step 3: The boot loader performs low-level CPU initialization. It initializes the CPU registers, which control where physical memory is mapped, the quantity of memory, and its speed.
Step 4: The boot loader initializes the flash file system on the system board.
Step 5: Finally, the boot loader locates and loads a default IOS operating system software image into memory and gives control of the switch over to the IOS.
S1(config)# boot system flash:/c2960-lanbasek9-mz.150-2.SE/c2960-lanbasek9-mz.150-2.SE.bin
88
What must be programmed on a switch to allow remote management? Provide an example set of commands.
To prepare a switch for remote management access, the switch must have a switch virtual interface (SVI) configured with an IPv4 address and subnet mask or an IPv6 address and a prefix length for IPv6.
S1# configure terminal
S1(config)# interface vlan 99
S1(config-if)# ip address 172.17.99.11 255.255.255.0
S1(config-if)# ipv6 address 2001:db8:acad:99::11/64
S1(config-if)# no shutdown
S1(config-if)# end
S1# copy running-config startup-config
S1# configure terminal
S1(config)# ip default-gateway 172.17.99.1
S1(config)# end
S1# copy running-config startup-config
S1# show ip interface brief
S1# show ipv6 interface brief
89
What is the purpose of the “mdix auto” command and when should it be used? A prerequisite for the command is that the interface speed and duplex settings must be set to auto-negotiate. Provide a full sample switch interface configuration example including speed, duplex, and mdix settings.
Until recently, certain cable types (straight-through or crossover) were required when connecting devices. Switch-to-switch or switch-to-router connections required using different Ethernet cables. Using the automatic medium-dependent interface crossover (auto-MDIX) feature on an interface eliminates this problem. When auto-MDIX is enabled, the interface automatically detects the required cable connection type (straight-through or crossover) and configures the connection appropriately. When connecting to switches without the auto-MDIX feature, straight-through cables must be used to connect to devices such as servers, workstations, or routers. Crossover cables must be used to connect to other switches or repeaters.
S1(config-if)# mdix auto
S1# show controllers ethernet-controller fa0/1 phy | include MDIX Auto-MDIX : On [AdminState=1 Flags=0x00052248]
S1# show interfaces fastEthernet 0/18 FastEthernet0/18 is up, line protocol is up (connected) Hardware is Fast Ethernet, address is 0025.83e6.9092 (bia 0025.83e6.9092) MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Full-duplex, 100Mb/s, media type is 10/100BaseTX
90
What is the difference between Telnet and SSH? Give an example set of commands that would be used to allow remote management of a switch using SSH.
SSH offers encrypted remote management. Telnet uses TCP port 23 and SSH uses TCP port 22
S1# show ip ssh
S1(config)# ip domain-name cisco.com
S1(config)# crypto key generate rsa
How many bits in the modulus [512]: 1024
```
S1(config)# username admin secret ccna
S1(config)# line vty 0 15
S1(config-line)# transport input ssh
S1(config-line)# login local
S1(config-line)# exit
S1(config)# ip ssh version 2
```
91
Describe the commands needed to secure the various means of access to a router? Give a sample configuration as an example.
```
Router# configure terminal
Router(config)# hostname R1
R1(config)# enable secret class
R1(config)# line console 0
R1(config-line)# password cisco
R1(config-line)# login
R1(config-line)# exit
R1(config)# line vty 0 4
R1(config-line)# password cisco
R1(config-line)# login
R1(config-line)# exit
R1(config)# service password-encryption
R1(config)#
R1(config)# banner motd #Authorized Access Only!#
R1(config)#
R1# copy running-config startup-config
```
92
What commands are needed to configure a router interface to work on both an IPv4 and IPv6 network? Give a sample configuration as an example.
Configured with at least one IP address - Use the ip address ip-address subnet-mask and the ipv6 address ipv6-address/prefix interface configuration commands.
R1(config)# interface gigabitethernet 0/0/0
R1(config-if)# ip address 192.168.10.1 255.255.255.0
R1(config-if)# ipv6 address 2001:db8:acad:1::1/64
R1(config-if)# description Link to LAN 1
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface gigabitethernet 0/0/1
R1(config-if)# ip address 192.168.11.1 255.255.255.0
R1(config-if)# ipv6 address 2001:db8:acad:2::1/64
R1(config-if)# description Link to LAN 2
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface serial 0/0/0
R1(config-if)# ip address 209.165.200.225 255.255.255.252
R1(config-if)# ipv6 address 2001:db8:acad:3::225/64
R1(config-if)# description Link to R2
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)#
93
How does a switch build its switching / forwarding table? Describe the process by which a switch forwards an incoming Ethernet frame. How does it differ when the destination is already in the MAC table versus when it is not? What does a switch do if it receives a broadcast or multicast frame?
It examines the source MAC address and if it is not in the routing table it adds that port. Then it examines the destination. If the port associated with the destination MAC address is in the table it will forward it to that port. If not, it will flood the frame out all ports.
This will differ based on whether it is a unicast, unknown unicast, multicast or broadcast frame.
94
Describe the different switching methods and rate their relative degree of latency they incur on forwarding Ethernet frames.
Store and Forward –
Error checking - After receiving the entire frame on the ingress port, the switch compares the frame check sequence (FCS) value in the last field of the datagram against its own FCS calculations. The FCS is an error checking process that helps to ensure that the frame is free of physical and data-link errors. If the frame is error-free, the switch forwards the frame. Otherwise, the frame is dropped.
Automatic buffering - The ingress port buffering process used by store-and-forward switches provides the flexibility to support any mix of Ethernet speeds. For example, handling an incoming frame traveling into a 100 Mbps Ethernet port that must be sent out a 1 Gbps interface would require using the store-and-forward method. With any mismatch in speeds between the ingress and egress ports, the switch stores the entire frame in a buffer, computes the FCS check, forwards it to the egress port buffer and then sends it.
Cut-through –
The store-and-forward switching method drops frames that do not pass the FCS check. Therefore, it does not forward invalid frames.
By contrast, the cut-through switching method may forward invalid frames because no FCS check is performed. However, cut-through switching has the ability to perform rapid frame switching. This means the switch can make a forwarding decision as soon as it has looked up the destination MAC address of the frame in its MAC address table, as shown in the figure.
95
What is a collision domain? What is a broadcast domain? How do each of the different kinds of intermediary devices (legacy hubs, switches, and routers) relate to collision and broadcast domains?
Collision Domain –
In legacy hub-based Ethernet segments, network devices competed for the shared medium. The network segments that share the same bandwidth between devices are known as collision domains. When two or more devices within the same collision domain try to communicate at the same time, a collision will occur.
If an Ethernet switch port is operating in half-duplex, each segment is in its own collision domain. There are no collision domains when switch ports are operating in full-duplex. However, there could be a collision domain if a switch port is operating in half-duplex.
Broadcast domain –
A collection of interconnected switches forms a single broadcast domain. Only a network layer device, such as a router, can divide a Layer 2 broadcast domain. Routers are used to segment broadcast domains, but will also segment a collision domain.
Hubs will increase the collision domain. Switches will increase the broadcast domain. Routers segment broadcast and collision domains.
96
Compare and contrast LANs and VLANs. When VLANs are configured on a network, what is their relationship to network broadcast domains, the subnetting scheme used, as well as network visibility (who may be seen)?
A VLAN creates a logical broadcast domain that can span multiple physical LAN segments. VLANs improve network performance by separating large broadcast domains into smaller ones. If a device in one VLAN sends a broadcast Ethernet frame, all devices in the VLAN receive the frame, but devices in other VLANs do not.
97
What is the significance of VLAN 1? Differentiate between the different types of VLANs including default, data, voice, management, and native VLANs.
VLAN 1 on a Cisco switch is the default VLAN. Therefore, all switch ports are on VLAN 1 unless it is explicitly configured to be on another VLAN. By default, all Layer 2 control traffic is associated with VLAN 1.
Important facts to remember about VLAN 1 include the following:
All ports are assigned to VLAN 1 by default.
The native VLAN is VLAN 1 by default.
The management VLAN is VLAN 1 by default.
VLAN 1 cannot be renamed or deleted.
Data VLANs are VLANs configured to separate user-generated traffic. They are referred to as user VLANs because they separate the network into groups of users or devices. A modern network would have many data VLANs depending on organizational requirements. Note that voice and network management traffic should not be permitted on data VLANs.
A separate VLAN is needed to support Voice over IP (VoIP). VoIP traffic requires the following:
Assured bandwidth to ensure voice quality
Transmission priority over other types of network traffic
Ability to be routed around congested areas on the network
Delay of less than 150 ms across the network
To meet these requirements, the entire network has to be designed to support VoIP.
A management VLAN is a data VLAN configured specifically for network management traffic including SSH, Telnet, HTTPS, HTTP, and SNMP. By default, VLAN 1 is configured as the management VLAN on a Layer 2 switch.
User traffic from a VLAN must be tagged with its VLAN ID when it is sent to another switch. A switch may also have to send untagged traffic across a trunk link. Untagged traffic is generated by a switch and may also come from legacy devices. The 802.1Q trunk port places untagged traffic on the native VLAN. The native VLAN on a Cisco switch is VLAN 1 (i.e., default VLAN).
It is a best practice to configure the native VLAN as an unused VLAN, distinct from VLAN 1 and other VLANs. In fact, it is not unusual to dedicate a fixed VLAN to serve the role of the native VLAN for all trunk ports in the switched domain.
98
Provide a sample set of commands that could be used to create and name a normal range VLAN as well as assign a switch port to that VLAN. Where does the VLAN configuration get stored on a Cisco 2960 switch? What command would be used to delete an individual VLAN? What command would be used to delete the entire VLAN database?
```
Create vlan:
S1# configure terminal
S1(config)# vlan 20
S1(config-vlan)# name student
S1(config-vlan)# end
```
Assign ports to vlan
Switch# configure terminal
Switch(config)# interface interface-id
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan vlan-id
Switch(config-if)# end
Deleting a single vlan: no vlan vlan-id
Deleting the vlan db: delete flash:vlan.dat
Configurations stored in flash memory
99
Describe what is meant by the term “VLAN Trunk” and identify the trunking protocol supported by the Cisco IOS. Provide a sample switch interface trunk configuration.
A VLAN trunk is a Layer 2 link between two switches that carries traffic for all VLANs (unless the allowed VLAN list is restricted manually or dynamically).
Switch# configure terminal
Switch(config)# interface interface-id
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk native vlan vlan-id
Switch(config-if)# switchport trunk allowed vlan vlan-list
Switch(config-if)# end
Cisco supports 802.1Q trunking encapsulation. Also Dynamic Trunking Protocol (DTP)
100
Describe the requirements of implementing Legacy inter-VLAN routing including the advantages/disadvantages of this approach. Provide an example configuration demonstrating the relevant switch and router commands needed.
The first inter-VLAN routing solution relied on using a router with multiple Ethernet interfaces. Each router interface was connected to a switch port in different VLANs. The router interfaces served as the default gateways to the local hosts on the VLAN subnet.
Legacy inter-VLAN routing using physical interfaces works, but it has a significant limitation. It is not reasonably scalable because routers have a limited number of physical interfaces. Requiring one physical router interface per VLAN quickly exhausts the physical interface capacity of a router.
101
Describe the requirements of implementing Router-on-a-Stick inter-VLAN routing including the advantages/disadvantages of this approach. Provide an example configuration demonstrating the relevant switch and router commands needed.
The ‘router-on-a-stick’ inter-VLAN routing method overcomes the limitation of the legacy inter-VLAN routing method. It only requires one physical Ethernet interface to route traffic between multiple VLANs on a network.
The configured subinterfaces are software-based virtual interfaces. Each is associated with a single physical Ethernet interface. Subinterfaces are configured in software on a router. Each subinterface is independently configured with an IP address and VLAN assignment. Subinterfaces are configured for different subnets that correspond to their VLAN assignment. This facilitates logical routing.
The router-on-a-stick method of inter-VLAN routing does not scale beyond 50 VLANs.
102
Describe the requirements of implementing inter-VLAN routing on a Layer 3 switch including the advantages/disadvantages of this approach. Provide an example configuration demonstrating the relevant Layer 3 switch commands needed.
The modern method of performing inter-VLAN routing is to use Layer 3 switches and switched virtual interfaces (SVI). An SVI is a virtual interface that is configured on a Layer 3 switch, as shown in the figure.
Inter-VLAN SVIs are created the same way that the management VLAN interface is configured. The SVI is created for a VLAN that exists on the switch. Although virtual, the SVI performs the same functions for the VLAN as a router interface would. Specifically, it provides Layer 3 processing for packets that are sent to or from all switch ports associated with that VLAN.
The following are advantages of using Layer 3 switches for inter-VLAN routing:
They are much faster than router-on-a-stick because everything is hardware switched and routed.
There is no need for external links from the switch to the router for routing.
They are not limited to one link because Layer 2 EtherChannels can be used as trunk links between the switches to increase bandwidth.
Latency is much lower because data does not need to leave the switch in order to be routed to a different network.
They more commonly deployed in a campus LAN than routers.
The only disadvantage is that Layer 3 switches are more expensive.
103
What show commands can be useful in diagnosing VLAN configuration, trunking, and Inter-VLAN routing issues? Describe the output given by each command.
Issue Type
How to Fix
How to Verify
Missing VLANs
Create (or re-create) the VLAN if it does not exist.
Ensure host port is assigned to the correct VLAN.
show vlan [brief]
show interfaces switchport
ping
Switch Trunk Port Issues
Ensure trunks are configured correctly.
Ensure port is a trunk port and enabled.
show interfaces trunk
show running-config
Switch Access Port Issues
Assign correct VLAN to access port.
Ensure port is an access port and enabled.
Host is incorrectly configured in the wrong subnet.
show interfaces switchport
show running-config interface
ipconfig
Router Configuration Issues
Router subinterface IPv4 address is incorrectly configured.
Router subinterface is assigned to the VLAN ID.
show ip interface brief
show interfaces
104
What is the purpose of the Spanning Tree Protocol? Describe the different switch port roles including root ports, designated ports, and alternate (blocked) ports.
Layer 2 loopback prevention protocol on ethernet LANs.
Root port: After the root bridge has been determined, the STA algorithm is used to select the root port. Every non-root switch will select one root port. The root port is the port closest to the root bridge in terms of overall cost (best path) to the root bridge. This overall cost is known as the internal root path cost.
Designated ports: All ports on the root bridge are designated ports, as shown in the figure. This is because the root bridge has the lowest cost to itself.
Blocked (alternate) ports: If a port is not a root port or a designated port, then it becomes an alternate (or backup) port. Alternate ports and backup ports are in discarding or blocking state to prevent loops.
105
Describe the root bridge election process. How can you ensure a switch will win the root bridge role? What is a BPDU and what is it used for?
The STA designates a single switch as the root bridge and uses it as the reference point for all path calculations. Switches exchange BPDUs to build the loop-free topology beginning with selecting the root bridge.
An election process determines which switch becomes the root bridge. All switches in the broadcast domain participate in the election process. After a switch boots, it begins to send out BPDU frames every two seconds. These BPDU frames contain the BID of the sending switch and the BID of the root bridge, known as the Root ID.
The switch with the lowest BID will become the root bridge. At first, all switches declare themselves as the root bridge with their own BID set as the Root ID. Eventually, the switches learn through the exchange of BPDUs which switch has the lowest BID and will agree on one root bridge.
The root bridge is selected by manually configuring its bridge priority to a low value. 32768 is the default value out of a range from 0 to 61440. If all switches in a single spanning tree have the same bridge priority, the switch with the lowest MAC address will become the root bridge.
106
What do the Portfast and BPDU Guard features do?
Port State
Description
Blocking
The port is an alternate port and does not participate in frame forwarding. The port receives BPDU frames to determine the location and root ID of the root bridge. BPDU frames also determine which port roles each switch port should assume in the final active STP topology. With a Max Age timer of 20 seconds, a switch port that has not received an expected BPDU from a neighbor switch will go into the blocking state.
Listening
After the blocking state, a port will move to the listening state. The port receives BPDUs to determine the path to the root. The switch port also transmits its own BPDU frames and informs adjacent switches that the switch port is preparing to participate in the active topology.
Learning
A switch port transitions to the learning state after the listening state. During the learning state, the switch port receives and processes BPDUs and prepares to participate in frame forwarding. It also begins to populate the MAC address table. However, in the learning state, user frames are not forwarded to the destination.
Forwarding
In the forwarding state, a switch port is considered part of the active topology. The switch port forwards user traffic and sends and receives BPDU frames.
Disabled
A switch port in the disabled state does not participate in spanning tree and does not forward frames. The disabled state is set when the switch port is administratively disabled.
RSTP Port States: Discarding, Learning, and Forwarding. Discarding takes place of disabled, blocking and listening.
107
What is the purpose of using EtherChannel and what are its advantages?
STP Variety
Description
STP
This is the original IEEE 802.1D version (802.1D-1998 and earlier) that provides a loop-free topology in a network with redundant links. Also called Common Spanning Tree (CST), it assumes one spanning tree instance for the entire bridged network, regardless of the number of VLANs.
PVST+
Per-VLAN Spanning Tree (PVST+) is a Cisco enhancement of STP that provides a separate 802.1D spanning tree instance for each VLAN configured in the network. PVST+ supports PortFast, UplinkFast, BackboneFast, BPDU guard, BPDU filter, root guard, and loop guard.
RSTP
Rapid Spanning Tree Protocol (RSTP) or IEEE 802.1w is an evolution of STP that provides faster convergence than STP.
802.1D-2004
This is an updated version of the STP standard, incorporating IEEE 802.1w.
Rapid PVST+
This is a Cisco enhancement of RSTP that uses PVST+ and provides a separate instance of 802.1w per VLAN. Each separate instance supports PortFast, BPDU guard, BPDU filter, root guard, and loop guard.
MSTP
Multiple Spanning Tree Protocol (MSTP) is an IEEE standard inspired by the earlier Cisco proprietary Multiple Instance STP (MISTP) implementation. MSTP maps multiple VLANs into the same spanning tree instance.
MST
Multiple Spanning Tree (MST) is the Cisco implementation of MSTP, which provides up to 16 instances of RSTP and combines many VLANs with the same physical and logical topology into a common RSTP instance. Each instance supports PortFast, BPDU guard, BPDU filter, root guard, and loop guard.
Cisco switches running IOS 15.0 or later, run PVST+ by default.
108
What are some of the EtherChannel implementation restrictions? What has to be the same on both sides of the EtherChannel? What happens if one link of a port group goes down?
Interface types cannot be mixed. For example, Fast Ethernet and Gigabit Ethernet cannot be mixed within a single EtherChannel.
Currently each EtherChannel can consist of up to eight compatibly-configured Ethernet ports. EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast EtherChannel) or 8 Gbps (Gigabit EtherChannel) between one switch and another switch or host.
The Cisco Catalyst 2960 Layer 2 switch currently supports up to six EtherChannels. However, as new IOSs are developed and platforms change, some cards and platforms may support increased numbers of ports within an EtherChannel link, as well as support an increased number of Gigabit EtherChannels.
The individual EtherChannel group member port configuration must be consistent on both devices. If the physical ports of one side are configured as trunks, the physical ports of the other side must also be configured as trunks within the same native VLAN. Additionally, all ports in each EtherChannel link must be configured as Layer 2 ports.
Each EtherChannel has a logical port channel interface, as shown in the figure. A configuration applied to the port channel interface affects all physical interfaces that are assigned to that interface.
109
What commands are used to create an LACP EtherChannel using two FastEthernet interfaces?
S1(config)# interface range FastEthernet 0/1 - 2
S1(config-if-range)# channel-group 1 mode active
S1(config-if-range)# exit
S1(config)# interface port-channel 1
S1(config)# switchport mode trunk
S1(config)# switchport trunk allowed vlan 1,2,20
110
What are the five original STP port states? How did that change in RSTP?
Port State
Description
Blocking
The port is an alternate port and does not participate in frame forwarding. The port receives BPDU frames to determine the location and root ID of the root bridge. BPDU frames also determine which port roles each switch port should assume in the final active STP topology. With a Max Age timer of 20 seconds, a switch port that has not received an expected BPDU from a neighbor switch will go into the blocking state.
Listening
After the blocking state, a port will move to the listening state. The port receives BPDUs to determine the path to the root. The switch port also transmits its own BPDU frames and informs adjacent switches that the switch port is preparing to participate in the active topology.
Learning
A switch port transitions to the learning state after the listening state. During the learning state, the switch port receives and processes BPDUs and prepares to participate in frame forwarding. It also begins to populate the MAC address table. However, in the learning state, user frames are not forwarded to the destination.
Forwarding
In the forwarding state, a switch port is considered part of the active topology. The switch port forwards user traffic and sends and receives BPDU frames.
Disabled
A switch port in the disabled state does not participate in spanning tree and does not forward frames. The disabled state is set when the switch port is administratively disabled.
RSTP Port States: Discarding, Learning, and Forwarding. Discarding takes place of disabled, blocking and listening.
111
Briefly describe the different spanning tree versions. Which one is running by default on Cisco switches?
STP Variety
Description
STP
This is the original IEEE 802.1D version (802.1D-1998 and earlier) that provides a loop-free topology in a network with redundant links. Also called Common Spanning Tree (CST), it assumes one spanning tree instance for the entire bridged network, regardless of the number of VLANs.
PVST+
Per-VLAN Spanning Tree (PVST+) is a Cisco enhancement of STP that provides a separate 802.1D spanning tree instance for each VLAN configured in the network. PVST+ supports PortFast, UplinkFast, BackboneFast, BPDU guard, BPDU filter, root guard, and loop guard.
RSTP
Rapid Spanning Tree Protocol (RSTP) or IEEE 802.1w is an evolution of STP that provides faster convergence than STP.
802.1D-2004
This is an updated version of the STP standard, incorporating IEEE 802.1w.
Rapid PVST+
This is a Cisco enhancement of RSTP that uses PVST+ and provides a separate instance of 802.1w per VLAN. Each separate instance supports PortFast, BPDU guard, BPDU filter, root guard, and loop guard.
MSTP
Multiple Spanning Tree Protocol (MSTP) is an IEEE standard inspired by the earlier Cisco proprietary Multiple Instance STP (MISTP) implementation. MSTP maps multiple VLANs into the same spanning tree instance.
MST
Multiple Spanning Tree (MST) is the Cisco implementation of MSTP, which provides up to 16 instances of RSTP and combines many VLANs with the same physical and logical topology into a common RSTP instance. Each instance supports PortFast, BPDU guard, BPDU filter, root guard, and loop guard.
Cisco switches running IOS 15.0 or later, run PVST+ by default.
112
Of the two EtherChannel negotiation protocols, PAgP and LACP, which one is a Cisco- proprietary protocol, and which one is part of an IEEE open standard? Compare and contrast the three PAgP and LACP modes?
PaGP is the Cisco proprietary protocol and LACP is part of the IEEE standard.
PaGP Modes: On, desirable, auto.
LACP: On, active, passive.
