1.01 VLAN
I. Implement and Troubleshoot Campus Infrastructure and Services
- VLAN
What is a VLAN?
The actual name is short for Virtual LAN. In simple terms a VLAN is a switched network that is segmented, in a logical sense, by function, department, or application. The VLAN is also independent of the actual physical LAN. Meaning all of the users on the VLAN do not have to be on the same physical LAN, but they do have to be in the same IP subnet. As an example, CompanyA can have their Marketing Department physically located on 3 different floors in the building, but from a switch standpoint they are all together.
If the Marketing and HR departments wanted to communicate with each other then traffic between their respective VLANs would need to be routed via Switch Virtual Interface or (SVI). Creating SVI seems to be pretty simple and straight forward, you give the interface a L3 address. One thing to keep in mind about a SVI is that it does not become active until it is associated with a physical port.
There are two types of VLAN ports that are of importance here; Access and Voice.
The Voice VLAN basically allows an access port to carry IP voice traffic from an IP phone. The Voice VLAN config is not supported on trunk ports. How is this done? An 802.1Q header is added to the Ethernet frame indicating the VLAN ID. The switch checks to see if the VLAN ID in the header matches what is configured on the interface, if so, the traffic is permitted.
Here’s an example of how to configure:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet1/0/1.640
Switch(config-if)# mls qos trust cos
Switch(config-if)# switchport voice vlan 640
Switch(config-if)# ip address 10.10.10.122 255.255.255.0
Switch(config-if)# end
The Voice VLAN will not show as UP until “voice vlan” has been assigned to the interfaces that the IP Phones are connected to.
Let me also note that I may be asked or told in the lab to ensure that my switch ports bypass the blocking, listening, and learning states which means that I will have to configure “spantree portfast” on the interface.
I am sure that I may have left something important out regarding VLAN, if so just drop me a quick reminder. Afterall, this is supposed to be a learning process right? ;-D
