So to configure a port on a switch as a trunk port supporting Cisco IP phones, you would do the following.
So firstly on our switch.
Well, in this case the 500, I'm going to type the command show VLAN.
Switch to see our VLANs.
As you can see here, we've got a default VLAN and we've got our voice VLAN which is VLAN.
Two all interfaces are currently in the native VLAN.
In other words, the default VLAN.
So going into global configuration mode, I can type the command interface range if 0/1/1 up to three.
And then I can type the command switch port.
Trunk encapsulation and then specify an encapsulation.
In the past, we may have chosen eesl or ed to one Q Cisco IP phones only support dot one.
Q So we're going to specify one key.
Then I'm going to say switchboard mode trunk.
To force these ports to trunk and then switchboard.
Trunk native vlan one.
Then I'm going to top switchboard voice VLAN and in our case it's VLAN two.
Topping the command do show run interface.
If 01/1 will show me the running configuration of that specific port.
Now remember, default commands don't show up in the running config, so you won't necessarily see all
the commands we've just typed because some of them are there by default.
But as you can see here, the port is trunking and the voice VLAN is VLAN two.
The problem here is that all VLANs will be allowed across this port, which could potentially cause
that issue where broadcasts affect the processing of Cisco IP phones.
So we should manually prune this trunk.
So I'm going to top the command switchboard trunk allowed VLAN and then I'm going to specify the VLANs
that are allowed.
Now on certain switches, you might only need to specify the voice VLAN, but in the U.S. 500 I'm going
to specify all the default vlans plus the voice vlan.
Not tapping the command du show run and the specific interface shows me that I'm only allowing the native
VLAN VLAN one on ethernet VLAN two, which is my voice VLAN and the other default VLANs supported on
Cisco switches.
So once again do show VLAN switch.
Will allow me to see those default VLANs one is the default for Ethernet and then we have the VLANs
for FTI and token ring.
So that's how you configure an interface to support trunking.
It's no longer recommended, but if you have an older switch, you may need to configure it in this
way.
Lastly, I could tap the command show interface f01/1 switchboard.
I notice you can see here that the administrative mode is shrunk.
The operational mode at the moment is trunk, encapsulation is dot one Q the native VLAN is VLAN one,
which is the default the VLANs enabled across this interface, all 1 to 1000 2 to 1005.
The active VLANs at the moment are VLANs one and two.
The voice VLAN is VLAN two.
The recommended way to implement IP phones in a network infrastructure is to use multiple VLAN access
ports.
In this example, we are configuring the port on the switch as an access port, but still configuring
two VLANs on that port.
The phone will be in the voice VLAN and the PC will be in the data VLAN.
Tag frames will be sent to the phone.
So 801 Q frames are still used.
Even though this is an access port untagged frames are sent to the PC.
Now this flies in the face of what you learned in the CNA course.
In the CNA course we learnt that an access port belongs to a single VLAN.
That is not the case in this scenario.
In this scenario, the access port has two VLANs configured on it.
Now there are multiple advantages to this method of implementation.
The first one is that a multi VLAN access port can be configured as a secure port, unlike the previous
example where we configured the port as a trunk.
The voice vlan id can also be discovered through CDP or LDAP, so the manual configuration of vlans
on the phone is not required.
It also allows for scalability from an IP addressing point of view.
The issue that you may encounter in the real world.
Is that if a Class C address has been allocated to your PCs and let's say using 80% of your addresses.
So 80% of the IP addresses in that subnet have been allocated to physical devices like PCs.
And now you add Cisco IP phones to the mix.
You are essentially doubling the amount of devices that you only have, 20% of the IP addresses remaining
in that subnet.
So you cannot put the phones and the PC in the same subnet without redoing your IP address.
However, if you put your phones into a separate subnet, that doesn't affect the IP addressing of the
PCs.
So you allocate a separate subnet for IP phones, and the IP subnet allocated to the PCS is left alone.
There's also a logical separation of voice and data traffic.
Because the phones are on a separate subnet to the PCs.
It's easier to implement quality of service.
It's easier to implement your access lists, and it's easier to implement security.
So that's a major advantage to separating the phones and the PCs into separate subnets.
Two devices can also be connected to a single port in the switch, which minimizes cabling.
Your PC is physically connected to the phone, which is physically connected to the switch across a
single cable.
However, logically, the phone and the PC are in separate cables because they are in different VLANs.
But physically you saving on cabling.
The multiple VLAN access port implementation tends to be the most common in the real world and is the
recommended way to implement IP phones to configure a multiple VLAN access port on an interface.
Do the following.
So on a U.S. 500 or on our switch I'm going to top the come on show VLAN switch to see the VLANs configured
at the moment we have vlan one configured on ports.
If 01/0 up to f01/8.
No interfaces are in the voice vlan.
I can also do the command show run interface if 01/1.
To show you the configuration on this interface.
As you can see, I've just defaulted the configuration.
All ports are in excess VLAN one.
So going into global config mode and tapping the command interface range of 01/1, two, three.
In other words, we're going to configure the three ports that have our IP phones connected to them.
I cannot type the command switch port mode access making these ports access ports, which is the default.
Then I can tap the command switchboard, the voice vlan two and switchboard access vlan one.
Now tapping the command show run interface.
If 011 shows me that that interface has been configured with a voice VLAN, we don't see the native
VLAN or the data VLAN or the access VLAN because VLAN one is the default VLAN and default configurations
don't show up in the running config, but tapping the command show interface if zero one says one switch
port.
Allows me to see the voice and data VLAN more clearly.
So on this interface it's been configured as a static access port and is acting as a static access port.
The access VLAN is VLAN one the default and notice the voice VLAN is VLAN two.
So even though the operational mode is static access, in other words, this is acting as an access
port.
We are allowing VLANs one and two across this port.
The fourth way to implement IP phones is to use ADA 2.1 P, now 82.1 P frames.
Use the three bits in the ADA 201 CU header to allow for the prioritization of voice traffic over data
traffic.
They are three bits in an edited or one Q header called the costs or class of service bits.
I'll talk more about these later.
Essentially Editor a1p allows for the marking of voice traffic with a value of five in the cost field,
allowing the switch to see voice traffic as higher priority than data traffic.
Now with a single VLAN access port using ADA or one P, the interface is in a single VLAN, so both
the phone and the PC are in VLAN two.
But the phone is going to send tagged frames to the switch now because this is a standard access port.
The phone uses a special VLAN number in the edited or one Q header to allow for the use of 80 21q frames.
Now just to recap from the CCNA course, a standard Ethernet frame has a source and destination field,
a length or either type the data and then a frame check sequence when edited or one Q is used.
A tag is inserted between the source and destination address and the length and either type field.
That tag consists of four bytes.
16 bits is the tag protocol identifier and then the remaining 16 bits consist of the priority code point
or priority field, the canonical format indicator and the vlan id now editor r1p specifies the meaning
of the priority field or class of service or cost field.
The priority code point field is three bits in length.
In other words, the binary values are from 000 to 111, and decimal values is 0 to 7.
The higher the priority value, the more important the traffic and thus voice will have a binary value
of 101 or the equivalent decimal value of five.
So the phone is sending edited or one q frames to the switch on an access port with the cost field or
priority code point field set to five.
In other words, it's sending an edit two to the one p frame to the switch.
Now just to reiterate terminology and edit 201q header is inserted in the Ethernet frame, which looks
as follows.
Edit 201p denotes the meaning or values of the priority field or cost field.
The value specified here form part of the recommendations of edit 2 to 1 p.
So once again editor or one P specifies the different classes or values of the priority field in an
802 to 1 Q header.
The phone is setting the value of the cost field to five when sending frames to the switch.
The switch therefore knows that traffic from the phone has a higher priority than traffic from the PC.
Now that explains how editorial one PPI can be used for quality of service.
But in this example, this is an access port.
In other words, it's not a trunk port, it's an access port.
Only one VLAN has been configured on this port.
VLAN two.
So when sending traffic to the switch, a VLAN number has to be specified by the phone and the VLAN
number used in this case is VLAN zero.
The switch therefore knows that when it receives an edit to the one Q frame with the VLAN number set
to zero that the phone still belongs to the VLAN configured on this port as the access VLAN.
So all traffic from the phone and the PC reside in VLAN two.
The phone is not in a separate VLAN to the PC.
They both belong to VLAN two.
Thus the use of the special VLAN of zero when sending ed or one q frames to the switch on this access
port.
So to configure ATO 2.1 p on an axis port, you need to do the following.
So before configuring the switch or the U.S. 500, let's have a look at our VLANs.
So as you can see here, all interfaces on the default VLAN of VLAN one.
Once again show run interface.
If 011 shows us that the interface has a default configuration on it.
Going into global config mode typing interface range f01/123.
The interfaces that have our phones connected to them.
I can tap the command switch port mode access so these ports are not going to be configured as trunks.
They configured as access ports.
Switch port.
Voice vlan dot one p to specify the use of dot one p on these ports switch port.
Access VLAN two.
Notice we're not specifying a voice vlan of two.
We are specifying an access vlan of two.
So once again, show run interface f01/1.
Shows me that this port is in VLAN two.
It's an access port, but we are using ED or one P on this interface.
The phones will transmit traffic to the switch as tagged frames using VLAN zero in the VLAN identifier.
Both the phone and the PC are in VLAN two.
That concludes part one of our discussion of the Cisco IP phone startup process.
We discussed how an IP phone obtains power, how VLAN information is provided to the phone using CDP
or LDPE.
In the next part, we're going to continue the discussion by looking at how an IP phone acquires an
IP address, downloads its firmware and configuration, and registers with a Q CM.
We'll also discuss the signaling protocols of skinny and sip.
Thank you for watching.