CCNA3 Exploration Chapter 3. Study questions. Answers
3.1
Why is it generally a good idea to split up a large network into smaller
networks?
Splits up broadcast domains, which cuts down traffic and should improve
performance. Allows different groups of users to have different facilities and
security regimes.
What is the advantage of implementing subnets as VLANs rather than using
routers to separate subnets?
VLANs can be implemented using switches, which are cheaper and operate
more quickly that routers. (Though a layer 3 device such as a router is still
needed to route traffic between VLANs.) A VLAN can be implemented across
several switches in different locations, so that a group of users with the same
requirements does not have to be all together in the same place.
How many VLANs can there be on a Catalyst 2600 series switch?
255
Which VLANs exist by default on a Catalyst 2600 switch, and which of these
are intended for Ethernet networks?
VLAN 1 is for Ethernet. VLANs 1002 to 1005 also exist, but are for use on
Token Ring or FDDI networks.
If you create a normal range VLAN, where will the information about it be
stored?
In a file called vlan.dat which is in flash memory. (Not in the running or startup
configuration.)
A new Catalyst switch has not yet been configured. Are the Ethernet ports
associated with any VLAN? If so, which one?
By default, all Ethernet ports are in VLAN 1.
Should you configure the switch IP address on VLAN 1?
You could, but it is better for security reasons to create another VLAN to be
the management VLAN and assign the IP address to it. This management
VLAN will be used only for managing the switch via Telnet, SSH or the web
based interface.
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What name is given to the type of VLAN that carries normal user traffic such
as files, downloads and e-mails?
Data VLAN or User VLAN.
Which type of VLAN needs special configuration so that its traffic has priority
over other traffic?
Voice VLAN.
What are the two methods of assigning an end device to a VLAN, and which
method is more common? (Assume that voice traffic is not required.)
Port based or static VLANs are configured on switch ports and a device
connecting to a port belongs to the VLAN configured on that port. Dynamic
VLANs assign devices to VLANs using the MAC addresses of the devices,
and these VLAN to MAC address matches need to be stored on a server.
Static VLANs are more common.
A PC attached to a switch sends out a broadcast ARP request. Which devices
will receive the ARP request?
Devices on the same VLAN as the PC.
Which devices allow inter-VLAN communication?
Routers or layer 3 switches.
What is a VLAN trunk?
A link that carries traffic for more than one VLAN. It is a point to point link
between two switches or between a switch and a router.
What is frame tagging?
It is a method of adding information to a frame to show which VLAN the frame
belongs to. It is used only on VLAN trunk links.
Which protocol is now most commonly used for frame tagging, and which
other protocol may still be in use?
IEEE 802.1Q is now the common protocol. Inter Switch Link (ISL) is a Cisco
proprietary protocol that is no longer supported by newer Cisco switches, but
may still be in use.
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What is the purpose of the EtherType field in a frame, which is set to the
hexadecimal value of 0x8100?
It signals to the device receiving the frame that this is a tagged IEEE 802.1Q
frame containing VLAN information. If the frame were untagged then the
device would find the length/type field in this position.
What does a switch port on a trunk link do if it receives a frame without a tag?
Forwards it on to the native VLAN. By default this is VLAN 1, but usually a
different native VLAN is configured on a trunk link.
Why can native VLANs and VLAN trunks give problems when Cisco devices
and non-Cisco devices are mixed on a network?
Cisco devices do not tag frames from the native VLAN when forwarding them
on a trunk link, but some non-Cisco devices do tag them. By default, Cisco
switches drop tagged frames destined for the native VLAN, so frames from
non-Cisco devices may be dropped.
How can you configure the fastethernet interface fa0/1 of switch SW1 to be a
trunk port?
SW1(config)#int fa0/1
SW1(config-if)#switchport mode trunk
How can you configure the fastethernet interface fa0/2 of switch SW1 to be a
port that handles traffic from one VLAN only?
SW1(config)#int fa0/2
SW1(config-if)#switchport mode access
What is the purpose of Dynamic Trunking Protocol?
It allows linked switches to negotiate on whether or not the link between them
is a trunk link.
Two switches are connected. If both ends of the link are ports in dynamic auto
mode, will the link be a trunk or not?
No, it will be an access link.
Two switches are connected. If both ends of the link are ports in dynamic
desirable mode, will the link be a trunk or not?
Yes, it will be a trunk link.
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What is the currently approved method of creating a VLAN, number 6, called
Finance, on switch SW1?
SW1(config)#vlan 6
SW1(config-vlan)#name Finance
SW1(config-vlan)#end
Which other mode could be used for creating a VLAN?
Database configuration mode. (You don’t go into global configuration mode.
Starting from privileged exec, you go straight into VLAN database mode. No
longer recommended.)
Which command will let you see a list of all existing VLANs and the ports that
are associated with each one?
Show vlan brief (or show vlan)
What information does the command “show vlan summary” give you?
It tells you how many VLANs there are on the switch. No VLAN numbers,
names or detail.
Which command would show you whether or not VLAN 4 is up?
Show int vlan 4
What is the effect of the commands:
SW1(config)#int fa0/12
SW1(config-if)#no switchport access vlan
SW1(config-if)#end
Interface fa 0/12 will be removed from its existing VLAN and returned to the
default VLAN. (VLAN 1 unless this has been changed.)
What is the effect of the commands:
SW1(config)#no vlan 7
SW1(config)#exit
VLAN 7 is deleted. If any ports are assigned to VLAN 7 then they will become
inactive. They need to be assigned to another VLAN before they can be used
again.
What is the effect of the command:
SW1(config)#delete flash:vlan.dat
The VLAN database in flash memory is deleted. When the switch is reloaded,
all configured VLAN information will have disappeared (you hope!).
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You configure interface Fa0/1 as follows:
SW1(config-if)#switchport mode trunk
Which is the native VLAN, and which VLANs can this interface handle?
VLAN 1 is the native VLAN. The trunk can handle traffic belonging to all
VLANs.
Which additional commands would you give to make VLAN 90 the native
VLAN and to permit traffic belonging to VLANs 3, 4 and 5 only?
SW1(config-if)#switchport trunk native vlan 90
SW1(config-if)#switchport trunk allowed vlan add 3,4,5
Which command would show you how interface Fa0/1 has been configured
for trunking?
SW1# show interfaces fa0/1 switchport
You give the commands:
SW1(config)#int fa0/1
SW1(config-if)#no switchport trunk allowed vlan
SW1(config-if)#end
Which VLAN traffic can now pass over the trunk link?
Traffic for all VLANs. (Default condition is restored.)
How can you stop interface Fa0/1 from being a trunk link?
SW1(config)#int fa0/1
SW1(config-if)#switchport mode access
SW1(config-if)#end
A trunk link is not working correctly. What should you check?
Have the ports at both ends of the link been configured with the same native
VLAN?
Are the ports at both ends of the link working as trunk links or is there a
problem with their modes? (E.g. one of them configured as an access port or
both of them in dynamic auto mode.)
Are all the required VLANs allowed on the trunk at both ends?
Do all the devices on a VLAN have addresses on the same subnet? (Easy to
get this wrong.)
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