CCNA3 Exploration Chapter 6. Study questions. Answers
6.1
How are VLANs and subnets related?
Each VLAN is associated with a different subnet, so each VLAN has its own
group of IP addresses.
How do hosts on one VLAN communicate with hosts on another VLAN?
The packets have to be routed from one VLAN (subnet) to another by using a
router (or a multilayer switch).
In traditional inter-VLAN routing, how is the switch linked to the router?
There is a separate link, switch port and router port for each VLAN. The
switch ports connected to the router are in access mode, not trunk mode.
What is “router on a stick” inter-VLAN routing?
There is one trunked link connecting the router to the switch, so that all the
VLANs use the same physical router port.
Can all routers make a trunked link to a switch?
Not all. It depends on the router IOS.
Each VLAN is a separate subnet, so each VLAN will need a different IP
address on the router. How can all the VLANs share one interface?
Several subinterfaces, one for each VLAN, are configured on one physical
interface, and each subinterface is given a different IP address.
Suppose that a PC is on VLAN 2. What default gateway should be configured
on the PC?
The address of the router interface connected to that VLAN, if traditional interVLAN routing is used, or the address of the router subinterface assigned to
that VLAN if router on a stick is used.
What is the VLAN number if a router subinterface is configured as follows?
R1(config)#int f0/0.2
R1(config-subif)#encapsulation dot1q 20
R1(config-subif)#ip address 172.17.2.1 255.255.255.0
R1(config-subif)#end
The VLAN number is 20
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Do you need to use the no shutdown command when configuring a router
subinterface?
No. The no shutdown command goes on the physical interface, not on the
subinterface.
What are the advantages and disadvantages of using “router on a stick” rather
than traditional inter-VLAN routing?
Using a single trunk link allows more VLANs to be added without the need for
extra physical interfaces. It is cheaper to use a single trunk link, because
routers with many interfaces are expensive. The physical cabling is simpler.
Subinterfaces share the interface bandwidth and this might create a
bottleneck. Not all routers are able to have subinterfaces configured for
VLANs. The configuration for a trunk link is a bit more complicated than
configuring separate interfaces.
6.2.1
Do you need to configure a routing protocol on a router that is used for interVLAN routing?
No. If all the VLANs are directly connected then it will not need a routing
protocol to route between them. Directly connected networks go into the
routing table automatically. A routing protocol will only be needed if more than
one router is involved.
When inter-VLAN routing is used, how are the switchports that link to the
router configured?
If traditional inter-VLAN routing is used, with a separate link for each VLAN,
then the switch port is in access mode and assigned to the appropriate VLAN.
If “router on a stick” is used, then the switch port is configured for trunking.
Which show command produces this type of output?
show interface fa0/4 switchport
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