Sunday, January 15, 2017


Voice Vlan Configuration

                           Now the we talked about the theory of Voice Vlans, let’s take a look at how to configure them and remember that, there are 3 approaches we can do a Single Vlan Access Port that was the least Desirable but in some cases, we said we might need to do a Single Vlan Access Port for both an IPPhone and attached PC, where sending traffic into the same Vlan
                          The second option was a Multi-Vlan Access Port that a special type of Access Port where Cisco says “you can have two Vlans on a single Access Port if and if one of those Vlans is to decleared to be a Voice Vlan” and our third option was to create a Trunk Port and we know that, Trunk Ports can carry traffic for lots of Vlans infect, that could be a challenge for Security reason for Quality of Service reason, we probably don’t want that trunk between the Phone and the Wiring Switch carrying traffic for all of our Vlans, really we wanna carrying traffic for couple of Vlans, the Voice Vlan of course to get the Phone and if we do have an attached PC, we want to be carrying traffic for the Native Vlan remember that, the Native Vlan is the Vlan on a DOT1Q trunk that does not have those 4 extra Tag Bytes we call it an Untagged Vlan that’s the Vlan of PC attached to our IPPhone, first let’s see how to setup a Single Vlan Access Port and we gonna be using this topology on Picture
                     Notice we have got Laptop running a software based IP Phone and it’s plugging into interface fast Ethernet 1/0/10 on Switch SW1, how would we set up a Single Vlan Access Port, let’s go into a global Configuration mode and
Ø  Sw1(config)#interface fastetherent 1/0/10
Ø  Sw1(config-if)#switchport mode access
Ø  Sw1(config-if)#switchport access vlan 300
                             But we said that with a Single Vlan Access Port if maybe we had third party IP Phone that was Plugin to this type of Port and that Third Party Phone did not support the concept of Voice Vlan having a Phone to send traffic to one Vlan and attached PC sending traffic to different Vlan, we said that even though we could not get the Vlan separation, there was still a way if the Phone or the software PC supported it to give Priority marking to that Voice traffic, it was a DOT1P marking, it’s very simple to set that up, we simply say
Ø  Sw1(config-if)#switchport voice vlan dot1p
                        We are saying if any traffic comes in with a DOT1P tag, that traffic is part of our Vlan Voice Vlan and the Priority marking can be embedded inside of those Tag Bytes, let’s setup another port fastetherent 1/0/11, let’s set it up as a Multi-Vlan Access Port, we go into an interface
Ø  Sw1(config)#interface fastetherent 1/0/11
Ø  Sw1(config-if)#switchport mode access
Now we can specify the two different Vlan’s that can be on that Port, that Data Vlan another words the Access Vlan and the Voice Vlan
Ø  Sw1(config-if)#switchport access vlan 300
Ø  Sw1(config-if)#switchport voice vlan 400
                        How does the Phone know that it’s the Voice Vlan, if we using Multi-Vlan Access Port Configuration CDP specifically CDPv2 is going to tell the attached Phonehere is your Voice Vlan you belong to Vlan 400” now when that Phone boots up and it does a DHCP Request out on the network to get it’s IP Address and other information but the way the Phone knows how to make a DHCP Request thanks to CDP Version 2 we said, if we are not running CDP though if we running LLDP-Med, this was not an option for instead we need to have a trunk Connection between our Switch and IP Phone, let’s see how to set that up using
Ø  Sw1(config)#interface fastetherent 1/0/12
Ø  Sw1(config-if)#switchport trunk encapsulation dot1q
Ø  Sw1(config-if)#switchport mode trunk
                         Now the we said this Port is a trunk we need to define what the Native Vlan remember, the Native Vlan that’s the Vlan in to which PC would belong, if we had a PC plugged into that IP Phone and we can specify that Vlan which is going to be Vlan 300 in our Case for the Data Vlan, we can specify that with a command
Ø  Sw1(config-if)#switchport trunk native vlan 300
Now let’s specify the Voice Vlan
Ø  Sw1(config-if)#switchport voice vlan 400
                      And this Configuration by itself would work however, we now have a trunk between this Cisco Catalyst Switch and the IP Phone and that trunk by default is gonna be carrying traffic for all of the Vlan we probably don’t want that let’s do Prun off the unneeded Vlan, remember our discussion of Vlan Pruning on Trunks
Ø  Sw1(config-if)#switchport trunk allowed 300,400
                            We have now configured 3 different Ports to connect out IP Phones and if we want to verify the configuration one of those ports, let’s do fastetherent 1/0/11 of an example
Ø  Sw1#show interfaces fastethernet 1/0/11 switchport
                            This is gonna give us information such as what kind of port is this, we can see this is an Access Vlan or the Data Vlan of 300 that’s not going to have any Tags on it, and we got a Vlan of 400 that’s the Voice Vlan it will be tagged, the Voice frames have 4 extra Bytes added.

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  1. Wow, there is a LOT of useful information on here. Just by following all the links, I can become a VOIP expert (once I learn to apply it all, of course). As AmA said, "wonderful job", and THANK YOU for all the work and effort it must have taken you!

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