Voice VLAN

Voice VLAN

The voice VLAN feature enables access ports to carry IP voice traffic from an IP phone. When the switch is connected to a Cisco IP Phone, the phone sends voice traffic with Layer 3 IP precedence and Layer 2 class of service (CoS) values, which are both set to 5 by default. 

Because the sound quality of an IP phone call can deteriorate if the data is unevenly sent, the switch supports quality of service (QoS)based on IEEE 802.1p CoS.

We are going to have a separate VLAN for Data and Voice.The reason for that:

1. Performance, by having VLAN separation
2. Security, no sniffing VOIP packet

In other words we will have a separate broadcast domain, separate subnet for voice traffic

 Different ways to set up VOIP

Single VLAN Access Port

1. The pc and the phone will be on the same VLAN 
2. Like the most access port is configure for only one VLAN (Phone and PC are members of the same VLAN).
3. You use them for a software-based or non-Cisco phones (Like Vonage).Maybe it's the same device that needs to use the same single access port (Laptop)
4. Allows the ip phone to mark  an IEEE802.1p marking
5. Can not get Quality of Service configuration

Class of Service (CoS) or Quality of Service (QoS) is a way to manage multiple traffic profiles over a network by giving certain types of traffic priority over others. For example you can give Voice traffic priority over other traffic.Cisco automatically sets COS frames as 5

 CoS is the classification of specific traffic (at layer 2) by manipulating the class of service bits (in the frame header). It effectively 'marks' the traffic so that QoS can use this classification  to actually manipulate the traffic according to your policy. Unlike QoS (Quality of Service) CoS does not offer guarantees with bandwidth or delivery time its based on a best effort basis. 

IEEE P802.1p  ; A layer 2 QOS marking similar to COS, that is sent over a non-trunk connection

COS uses some bytes to identify some frames like a VLAN ID, 802.1p don't do that.

MultiVlan Access Port 

1. It's an access port
2. Can not support two VLANs at once ( or data frames or voice frames)
3. The switch will send CDP message version 2 request to discover what kind or frame is it
4. It wont work with LLDP-Med
5. If you do a packet capture , frames will look like dot1q trunk frames 
6. Frames going to the phone are going to be tag
7. The data is going to be a untag VLAN
8. Od cat switches wont support multivlan  access port

Trunk port

 Trunk Port

1.  Trunk port
2. Can carry traffic to multiple VLAN
3.  Compatible with LLDP-Med or CDP
4. Frames are dot1q frames
5. Because it's a trunk you "could" catch all type of frames because it's trunk (unicast, broadcast etc), you could have extra traffic
6.  We should prune all those VLANs for security and perspective

 Native VLAN:

If we need traffic going to our PC we will need a native VLAN, the untaged VLAN, the PC attached from our PC to our IP phone.

The native VLAN is the only VLAN which is not tagged in a trunk, in other words, native VLAN frames are transmitted unchanged.

Per default the native VLAN is VLAN 1 

 We will use this graphic for demonstration purpose only:

 Single VLAN access port:

  Only ONE Vlan , for a software-based ip phone

Now we will set another port 

MultiVLAN Access Port

Trunk

And this is what we can see..Fa0/22  Important and useful 
information

This exercise was successfully done!

:)