Chapter 9 - Implementing Ethernet Virtual LANs Flashcards
How would you create 2 broadcast domains on one switch?
Configure VLANs on the switch.
What are some common reasons for implementing VLANs?
1) Reduce CPU overhead on each device since less devices will receive broadcast frames
2) Reduce security risks by reducing the # of hosts that receive frames.
3) Improve security for hosts that send sensitive data by keeping them on a separate VLAN.
4) Create more flexible designs by grouping users by departments, or groups that work together.
5) To solve problems more quickly, since failures usually are problems experiences by devices in the same broadcast domain.
6) Reduce workload for the Spanning Tree Protocol (STP).
When using VLANs in networks that have multiple interconnected switches, what needs to be used on the links between the switches?
VLAN trunking
What is VLAN tagging?
The switch adds another header to the frame before sending it over the trunk. This extra header includes a VLAN identifier.
What is the purpose of the VLAN identifier?
So the sending and receiving switch can associate the frame with a particular VLAN ID and know which VLAN the frame belongs.
What are two trunking protocols that Cisco supports and which one is the most current one?
Inter-Switch Link (ISL) and IEEE 802.1Q (which is the newer standard)
What size VLAN header does 802.1Q add to the original frame’s Ethernet header?
4-bytes
What’s the size of the actual VLAN ID in the 802.1Q tag?
12 bits
Since the Layer 2 switch does not forward frames outside a VLAN, where does the job of forward data between VLANs fall?
Falls with routers.
In regards to routing between VLANs, instead of the router connecting an interface to each VLAN on the switch, what can be configured so the router only needs to use one interface connected to the switch?
Use trunking between the router and a switch. This is also known as router-on-a-stick.
Other than a router doing all the VLAN routing, what else can be considered when routing between VLANs?
Layer 3 switch
What are nontrunking interfaces on a switch also known as?
access interfaces
From configuration mode, what is the command to add a vlan?
vlan {vlan-id}
What optional command would give the VLAN a name?
name {name} VLAN subcommand
If you do not give a VLAN a name, what’s the format that is given by the switch?
VLANZZZZ where ZZZZ is the 4-digit decimal VLAN ID
After moving into the interface, what command would you use to assign that interface to a specific VLAN?
switchport access vlan {id-number}
What optional command do you use to disable trunking on an interface after assigning it to a VLAN?
switchport mode access - this prevents it from negotiating to trunk
How many VLANs does the 802.1Q header support?
4094 {0 and 4095 are reserved}
Cisco switches break the range of VLAN IDs into what 2 ranges?
normal and extended range - the normal range is from 1-1005 - the extended is from 1006 to 4094
What are the 4 command options for the switchport mode command?
1) access
2) trunk
3) dynamic desirable
4) dynamic auto
Which switchport mode command option always acts like a trunk port?
trunk
Which switchport mode command option initiates negotiation messages and responds to negotiation messages to dynamically choose whether to start using trunking?
dynamic desirable
Which switchport mode command option always acts like an access (nontrunk) port?
access
Which switchport mode command option passively waits to receive trunk negotiation messages?
dynamic auto
What is the default switchport mode on a switch?
dynamic auto
If the administrative mode is “access” on one side and “access” on the other side, what is the result?
access
If the administrative mode is “dynamic auto” on one side and “dynamic auto” on the other side, what is the result?
access
If the administrative mode is “dynamic auto” on one side and “dynamic desirable” on the other side, what is the result?
trunk
If the administrative mode is “access” on one side and “dynamic desirable” on the other side, what is the result?
access
What configuration of administrative mode do you not want to use?
trunk on one side and access on the other
Which command allows you to control what VLANs are allowed on the trunk?
switchport trunk allowed vlan {add | all | except | remove} vlan-list
What are 5 reasons why a switch would prevent a particular VLAN traffic from crossing a trunk?
1) A VLAN has been removed from the trunk’s allowed VLAN list.
2) A VLAN does not exist in the switch’s configuration
3) A VLAN does exist, but has been administratively shut down
4) A VLAN has been automatically pruned by VTP.
5) A VLAN’s STP instance has placed the trunk interface into a blocking state.
