Chapter 8 VLANS Flashcards
What’s a VLAN?
A virtual switch within a switch or domain of its own with its own broadcast.
What are some benefits to having VLANS?
- Smaller broadcast domains. Less end devices that have to use CPU recourse on broadcasts hence higher CPU over head.
- Security by not all host receiving every Frame despite being in the same switch.
- Flexible design without bring another physical switch to separate devices.
- Reduced STP workload by limiting VLAN to single access switch.
What is VLAN Trunking.
Allows multiple VLANs to pass through one interface (connection) into another switch.
What is VLAN tagging?
The Frame gets a Tag header added on when passing through a trunk, this leaves it with a VLAN ID so the switch receiving the traffic knows where what VLAN the frame belongs to.
How many bytes are in the Tag header and how many of them are the VLAN identifier
4 bytes in total and the VLAN ID has 12 Bits.
How big can a VLAN theoretically be? but how big is it actually and what is the range?
4096 this includes 0, but only 4094 can be used because 0 and 4095 are reserved so the true range is 1-4094
What is the current Trunking protocol?
802.1q standardized by IEEE
what are the two VLAN ranges in Cisco.
- Normal Range : 1-1005
- Extended Range: 1006-4094
- All Switches can use the normal range, Only some switches can use the extended range is determined by the configuration of VTP VLAN Trunking Protocol)
When is the 802.1Q header added? and removed?
- To the Frame right before the Frame leaves the Switch it originated.
- Removed as the header comes in on the other end of the receiving switch and once the switch has read the VLAN ID and it knows what VLAN to forward that frame.
Do devices that have received Frames that came from a Trunk see the 802.1Q header?
No, because the switch removes it as it comes in right before it passes.
What is a Native VLAN. What’s the default ID?
- Its a special VLAN ID on each trunk.
- The default ID is 1.
How do Trunk VLANs tag anything that is in the Native VLAN?
- By definition 802.1Q does not tag an 802.1Q tag on its Native VLAN. This means anything in the native VLAN does not carry a VLAN ID header in its frame
What does a VLAN Trunk do with a frame that comes in without an 802.1Q header on its frame?
It puts it on its Native VLAN.
What’s an important thing about Native VLANS when setting up VLAN Trunks?
Both ends of the VLAN Trunks must have the same Native VLAN.
Create a VLAN 2, Name it and assign ports Gi 0/1 - 0/3 access to the VALN just created.
Switch>
Switch>en
Switch#config ter
Switch(config)#vlan 2
Switch(config-vlan)#name Accounting
Switch(config-vlan)#exit
Switch(config)#interface range gi 0/1 - 3
Switch(config-if-range)#switchport access vlan 2
Switch(config-if-range)#switchport mode access
Switch(config-if-range)#exit
Switch(config)#
