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[Part 1 - Q#1]

Name the three reasons why a port is placed in forwarding state as a result of spanning tree.

[Part 1 - Q#1]

First, all ports on the root bridge are placed in forwarding state. Second, one port on each bridge is considered its root port, which is placed in forwarding state. Finally, on each LAN segment, one bridge is considered to be the designated bridge on that LAN; that designated bridge’s interface on the LAN is placed in a forwarding state.

[Part 1 - Q#2]

If two Cisco LAN switches are connected using Fast Ethernet, what VLAN trunking protocols could be used? If only one VLAN spanned both switches, is a VLAN trunking protocol needed?

[Part 1 - Q#2]

ISL and 802.1q are the trunking protocols used by Cisco over Fast Ethernet. If only one VLAN spans the two switches, a trunking protocol is not needed. Trunking or tagging protocols are used to tag a frame as being in a particular VLAN; if only one VLAN is used, tagging is unnecessary.

[Part 1 - Q#3]

What is the acronym and complete name of Cisco’s proprietary trunking protocol over Ethernet?

[Part 1 - Q#3]

Inter-Switch Link (ISL).

[Part 1 - Q#4]

Consider the phrase “A VLAN is a broadcast domain is an IP subnet.” Do you agree or disagree? State your reasons.

[Part 1 - Q#4]

From one perspective, the statement is false because an IP subnet is a Layer 3 protocol concept, and a broadcast domain and VLAN are Layer 2 concepts. However, the devices in one broadcast domain comprise the exact same set of devices that would be in the same VLAN and in the same IP subnet.

[Part 1 - Q#5]

What fields are added or changed in an Ethernet header when using 802.1q? Where is the VLAN ID in those fields?

[Part 1 - Q#5]

A new 4-byte 802.1q header, which includes the VLAN ID, is added after the source MAC address field of the original Ethernet frame. The original FCS field in the Ethernet trailer is modified because the value must be recalculated as a result of changing the header.

[Part 1 - Q#6]

Describe how a switch decides whether it should forward a frame, and tell how it chooses the output interface.

[Part 1 - Q#6]

The switch examines the frame’s destination MAC address and looks for the address in its bridge (or address) table. If it’s found, the matching entry tells the switch which output interface to use to forward the frame. If it isn’t found, the switch forwards the frame out all the other interfaces (except for interfaces blocked by spanning tree and the interface in which the frame was received). The switch table is built by examining incoming frames’ source MAC addresses.

[Part 1 - Q#7]

How does a switch build its address table?

[Part 1 - Q#7]

The switch listens for incoming frames and examines the source MAC address. If it isn’t in the table, the source address is added, along with the port (interface) on which the frame entered the switch. The switch also marks an entry for freshness so that entries can be removed after a period of disuse. This reduces table size and allows for easier table changes in case a spanning tree change forces moresignificant changes in the switch (address) table.

[Part 1 - Q#8]

What routing protocol does a transparent bridge use to learn about Layer 3 address groupings?

[Part 1 - Q#8]

None. Bridges do not use routing protocols. Transparent bridges do not care about Layer 3 address groupings. Devices on either side of a transparent bridge are in the same Layer 3 group—in other words, the same IP subnet.

[Part 1 - Q#9]

What settings does a bridge or switch examine to determine which should be elected as root of the spanning tree?

[Part 1 - Q#9]

The bridge priority is examined first (the lowest wins). In case of a tie, the lowest MAC address wins. The priority is prepended to the bridge ID in the actual BPDU message so that the combined fields can be compared easily.

[Part 1 - Q#10]

If a switch hears three different hello BPDUs from three different neighbors on three different interfaces, and if all three specify that Bridge 1 is the root, how does the switch choose which interface is its root port?

[Part 1 - Q#10]

The root port is the port on which the BPDU with the lowest-cost value is received. The root port is placed in forwarding state on each bridge and switch.

[Part 1 - Q#11]

Can the root bridge/switch ports be placed in blocking state?

[Part 1 - Q#11]

The root bridge’s ports are always in forwarding state because they always have cost 0 to the root, which ensures that they are always the designated bridges on their respective LAN segments.

[Part 1 - Q#12]

Describe the benefits of Spanning Tree Protocol as used by transparent bridges and switches.

[Part 1 - Q#12]

Physically redundant paths in the network are allowed to exist and be used when other paths fail. Also, loops in the bridged network are avoided. Loops are particularly bad because bridging uses LAN headers, which do not provide a mechanism to mark a frame so that its lifetime can be limited; in other words, the frame can loop forever.

[Part 1 - Q#13]

When a bridge or switch using Spanning Tree Protocol first initializes, what does it assert should be the tree’s root?

[Part 1 - Q#13]

Each bridge/switch begins by sending BPDUs claiming itself as the root bridge.

[Part 1 - Q#14]

Name the three reasons why a port is placed in forwarding state as a result of spanning tree.

[Part 1 - Q#14]

First, all ports on the root bridge are placed in forwarding state. Second, one port on each bridge is considered its root port, which is placed in forwarding state. Finally, on each LAN segment, one bridge is considered the designated bridge on that LAN; that designated bridge’s interface on the LAN is placed in forwarding state.

[Part 1 - Q#15]

Name the three interface states that Spanning Tree Protocol uses, other than forwarding. Which of these states is transitory?

[Part 1 - Q#15]

Blocking, listening, and learning. Blocking is the only stable state; the other two are transitory between blocking and forwarding. Table 2-2 summarizes the states and their features.

[Part 1 - Q#16]

What are the two reasons that a nonroot bridge/switch places a port in forwarding state?

[Part 1 - Q#16]

If the port is the designated bridge on its LAN segment, the port is placed in forwarding state. Also, if the port is the root port, it is placed in forwarding state. Otherwise, the port is placed in blocking state.

[Part 1 - Q#17]

Which two 2950 series EXEC commands list information about an interface’s spanning-tree state?

[Part 1 - Q#17]

The show spanning-tree command lists details of the current spanning tree for all VLANs, including port status. show spanning-tree interface x/y lists the details just for interface x/y.

[Part 1 - Q#18]

Define broadcast domain.

[Part 1 - Q#18]

A broadcast domain is a set of Ethernet devices for which a broadcast sent by any one of them should be received by all others in the group. Unlike routers, bridges and switches do not stop the flow of broadcasts. Two segments separated by a router would each be in a different broadcast domain. A switch can create multiple broadcast domains by creating multiple VLANs, but a router must be used to route packets between the VLANs.

[Part 1 - Q#19]

Define VLAN.

[Part 1 - Q#19]

A virtual LAN consists of a set of devices in the same broadcast domain, typically implemented by configuring one or more switches to place a set of switch interfaces, and their attached devices, into the same VLAN/broadcast domain. Broadcasts from one VLAN are not forwarded to other VLANs; unicasts between VLANs must use a router. Advanced methods, such as Layer 3 switching, can be used to allow the LAN switch to forward traffic between VLANs without each individual frame’s being routed by a router. However, for the depth of CCNA, such detail is not needed.

[Part 1 - Q#20]

If two Cisco LAN switches are connected using Fast Ethernet, what VLAN trunking protocols can be used? If only one VLAN spans both switches, is a VLAN trunking protocol needed?

[Part 1 - Q#20]

ISL and 802.1q are the trunking protocols that Cisco uses over Fast Ethernet. If only one VLAN spans the two switches, a trunking protocol is not needed. Trunking or tagging protocols are used to tag a frame as being in a particular VLAN; if only one VLAN is used, tagging is unnecessary.

[Part 1 - Q#21]

Define VTP

[Part 1 - Q#21]

VLAN Trunking Protocol transmits configuration information about VLANs between interconnected switches. VTP helps prevent misconfiguration, eases switch administration, and reduces broadcast overhead through the use of VTP pruning.

[Part 1 - Q#22]

Name the three VTP modes. Which mode does not allow VLANs to be added or modified?

[Part 1 - Q#22]

Server and client modes are used to actively participate in VTP; transparent mode is used to simply stay out of the way of servers and clients while not participating in VTP. Switches in client mode cannot change or add VLANs.

[Part 1 - Q#23]

What type of VTP mode allows a switch to create VLANs and advertise them to other switches?

[Part 1 - Q#23]

Only VTP servers can create and advertise VLANs with VTP.

[Part 1 - Q#24]

Must all members of the same VLAN be in the same collision domain, the same broadcast domain, or both?

[Part 1 - Q#24]

By definition, members of the same VLAN are all part of the same broadcast domain. They might all be in the same collision domain, but only if all devices in the VLAN are connected to hubs.

[Part 1 - Q#25]

What is Cisco’s proprietary trunking protocol over Ethernet?

[Part 1 - Q#25]

Inter-Switch Link (ISL)

[Part 1 - Q#26]

Explain the benefits provided by VTP pruning.

[Part 1 - Q#26]

VTP pruning reduces network overhead by preventing broadcasts and unknown unicast frames in a VLAN from being sent to switches that have no interfaces in that VLAN.

[Part 1 - Q#27]

What fields are added or changed in an Ethernet header when you use 802.1q? Where is the VLAN ID in those fields?

[Part 1 - Q#27]

A new 4-byte 802.1q header that includes the VLAN ID is added after the source MAC address field. The original FCS field in the Ethernet trailer is modified, because the value must be recalculated as a result of changing the header.

[Part 1 - Q#28]

Explain how a switch in VTP transparent mode treats VTP messages received from a VTP server.

[Part 1 - Q#28]

A switch in VTP transparent mode receives the VTP messages and forwards them as broadcasts. However, the switch ignores the contents of the messages, so it does not learn any VLAN information from the messages.

[Part 1 - Q#29]

What command on a 2950 switch creates VLAN 5? What configuration mode is required?

[Part 1 - Q#29]

In VLAN database configuration mode, the vlan 5 name newvlan5 command would create the new vlan, and give it a name.

[Part 1 - Q#30]

What command on a 2950 switch puts an interface into VLAN 5? What configuration mode is required?

[Part 1 - Q#30]

In interface configuration mode for that interface, the command switchport access vlan 5 assigns the interface to VLAN 5.

[Part 1 - Q#31]

Describe the basic differences in the processes used by VLAN configuration mode and the normally used configuration mode.

[Part 1 - Q#31]

In VLAN configuration mode, the commands do not take immediate effect. You must exit configuration mode or use the apply command to cause the configuration to be accepted.

[Part 1 - Q#32]

Give the correct syntax for the commands that put an interface into the various trunking modes, and identify which commands work when the switch on the other side of the link uses the auto option.

[Part 1 - Q#32]

switchport mode dynamic desirable
switchport mode dynamic auto
switchport mode trunk
switchport mode access
The first and third commands work with auto set on the other side of the link.

[Part 1 - Q#33]

What 2950 show commands list trunk status, both configured and operational?

[Part 1 - Q#33]

show interfaces fastethernet 0/x switchport
show interfaces fastethernet 0/x trunk

[Part 2 - Q#1]

Name the parts of an IP address.

[Part 2 - Q#1]

Network, subnet, and host are the three parts of an IP address. However, many people commonly treat the network and subnet parts as a single part, leaving only two parts, the subnet and host. On the exam, the multiple-choice format should provide extra clues as to which terminology is used.

[Part 2 - Q#2]

Define subnet mask. What do the bits in the mask whose values are binary 0 tell you about the corresponding IP address(es)?

[Part 2 - Q#2]

A subnet mask defines the number of host bits in an address. The bits of value 0 define which bits in the address are host bits. The mask is an important ingredient in the formula to dissect an IP address. Along with knowledge of the number of network bits implied for Class A, B, and C networks, the mask provides a clear definition of the size of the network, subnet, and host parts of an address.

[Part 2 - Q#3]

Given the IP address 10.5.118.3 and the mask 255.255.0.0, what is the subnet number?

[Part 2 - Q#3]

The subnet number is 10.5.0.0.

[Part 2 - Q#4]

Given the IP address 190.1.42.3 and the mask 255.255.255.0, what is the subnet number?

[Part 2 - Q#4]

The subnet number is 190.1.42.0. The binary algorithm math is shown in the following table.

[Part 2 - Q#5]

Given the IP address 140.1.1.1 and the mask 255.255.255.248, what is the subnet number?

[Part 2 - Q#5]

The subnet number is 140.1.1.0. The following subnet chart helps you learn how to calculate the subnet number without binary math. The magic number is 256 – 248 = 8.

[Part 2 - Q#6]

Given the IP address 167.88.99.66 and the mask 255.255.255.192, what is the subnet number?

[Part 2 - Q#6]

The subnet number is 167.88.99.64. The following subnet chart helps you learn how to calculate the subnet number without binary math. The magic number is 256 – 192 = 64.

[Part 2 - Q#7]

Given the IP address 10.5.118.3 and the mask 255.255.0.0, what is the broadcast address?

[Part 2 - Q#7]

The broadcast address is 10.5.255.255. The binary algorithm math is shown in the following table.

[Part 2 - Q#8]

Given the IP address 190.1.42.3 and the mask 255.255.255.0, what is the broadcast address?

[Part 2 - Q#8]

The broadcast address is 190.1.42.255. The binary algorithm math is shown in the following table.

[Part 2 - Q#9]

Given the IP address 140.1.1.1 and the mask 255.255.255.248, what is the broadcast address?

[Part 2 - Q#9]

The broadcast address is 140.1.1.7. The binary algorithm math is shown in the following table.

[Part 2 - Q#10]

Given the IP address 167.88.99.66 and the mask 255.255.255.192, what is the broadcast address?

[Part 2 - Q#10]

The broadcast address is 167.88.99.127. The binary algorithm math is shown in the following table.

[Part 2 - Q#11]

Given the IP address 10.5.118.3 and the mask 255.255.0.0, what are the assignable IP addresses in this subnet?

[Part 2 - Q#11]

The subnet number is 10.5.0.0, and the subnet broadcast address is 10.5.255.255. The assignable addresses are all the addresses between the subnet and broadcast addresses—namely, 10.5.0.1 to 10.5.255.254.

[Part 2 - Q#12]

Given the IP address 190.1.42.3 and the mask 255.255.255.0, what are the assignable IP addresses in this subnet?

[Part 2 - Q#12]

The subnet number is 190.1.42.0, and the subnet broadcast address is 190.1.42.255. The assignable addresses are all the addresses between the subnet and broadcast addresses—namely, 190.1.42.1 to 190.1.42.254.

[Part 2 - Q#13]

Given the IP address 140.1.1.1 and the mask 255.255.255.248, what are the assignable IP addresses in this subnet?

[Part 2 - Q#13]

The subnet number is 140.1.1.0, and the subnet broadcast address is 140.1.1.7. The assignable addresses are all the addresses between the subnet and broadcast addresses—namely, 140.1.1.1 to 140.1.1.6.

[Part 2 - Q#14]

Given the IP address 167.88.99.66 and the mask 255.255.255.192, what are the assignable IP addresses in this subnet?

[Part 2 - Q#14]

The subnet number is 167.88.99.64, and the subnet broadcast address is 167.88.99.127. The assignable addresses are all the addresses between the subnet and broadcast addresses—namely, 167.88.99.65 to 167.88.99.126.

[Part 2 - Q#15]

Given the IP address 10.5.118.3 and the mask 255.255.255.0, what are all the subnet numbers if the same (static) mask is used for all subnets in this network?

[Part 2 - Q#15]

The numbers are 10.0.0.0 (zero subnet),10.0.1.0, 10.0.2.0, 10.0.3.0, and so on, up to 10.255.254.0 and 10.255.255.0 (broadcast subnet). The Class A network number is 10.0.0.0. The mask implies that the entire second and third octets, and only those octets, comprise the subnet field. The first subnet number, called the zero subnet (10.0.0.0), and the last subnet number, called the broadcast subnet (10.255.255.0), may be used.

[Part 2 - Q#16]

How many IP addresses can be assigned in each subnet of 10.0.0.0, assuming that a mask of 255.255.255.0 is used? If the same (static) mask is used for all subnets, how many subnets are there?

[Part 2 - Q#16]

There are 2number-of-host-bits, or 28, hosts per subnet, minus two special cases. The number of subnets is 2number-of-subnet-bits, or 216.

[Part 2 - Q#17]

How many IP addresses can be assigned in each subnet of 140.1.0.0, assuming that a mask of 255.255.255.248 is used? If the same (static) mask is used for all subnets, how many subnets are there?

[Part 2 - Q#17]

There are 2number-of-host-bits, or 23, hosts per subnet, minus two special cases. The number of subnets is 2number-of-subnet-bits, or 213.

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