Wednesday, June 30, 2010

CCNA Voice 07

There are a few steps to set up a Cisco IP phone to work with your network. Like any other IP devices, the first step is to provide addressing. This provision comes in the form of DHCP. However there are several concepts that need to be in place first.
Take a look at the following diagram:

At this point it may seem confusing as to why the PC is connected to the phone instead of the switch. The reason why the PC is connected to the phone is because a Cisco IP phone is actually a 3-port switch! Internally it actually looks like this:

Switches speak the 802.1Q language of love, so it can tag its own packets. Packets originating from the IP Phone will be tagged with the VLAN number we'll be configuring later, and packets from the PC will be untagged, putting it in the native VLAN of the access port.

We'll first work on configuring the Voice VLAN from the switchport interface. Suppose that the IP Phone is connected to the F0/1 port of the switch, we'll have the configuration:
vlan 10
vlan 100
in f1/0
sw m a
sw a v 10
sw voice vlan 100
span port

Now suppose that the router is connected to F1/15. The router here will be our Call Manager and DHCP, so we'll set the switchport as follows:
in f1/15
sw m t

And then we'll the following configuration on the router:
in f0/0.10
encap dot 10
ip add
in f0/0.100
ip add
encap dot 100
in f0/0
no shut

Now that the router is able to reach both the Clients and the IP Phone subnets, it's time to set up the DHCP:
ip dhcp pool CLIENTS
ip dhcp pool IP_PHONES
option 150 ip

Notice that we put in an option 150 for the IP_PHONES scope. Option 150 is used by Cisco IP Phones to contact the (TFTP) server for configurations and/or upgrades to successfully boot.

At this point I'll show you the full topology. This is what we'll be working with:

We'll now work to set up IP telephony services. To do this, we'll begin with the basic command to get into telephony prompt:

At this point, we would not be able to create ephones and ephone-dns because by default the maximum for both is set to 0. An ephone-dn is typically a number and an ephone is what the number is assigned to. An ephone represents a single physical phone and can be automatically assigned or assigned based on a specified MAC address. You can have multiple ephone-dns assigned to one phone in a variety of ways. To allow creation of ephones and ephone-dns, type:
max-ephones 10
max-dn 10

Right now you would be able to allow up to 10 IP Phones (ephones), and they can share as many as 10 numbers (ephone-dns). However, do not exit the prompt yet, we should have to set the Call Manager which phones need to communicate through Skinny with. To do this, we'll type:
ip source-address port 2000

The port can be anything from 2000 to 9999. The default for Skinny is 2000 and we'll stick with that. Now we'll create a number (ephone-dn). We'll need to come up with a numbering plan. Everything in Site A will be using ranges 1001 to 1009, and anything from Site B will be 2001 to 2009. So we'll create a ephone-dn for our first phone like this:
ephone-dn 1
number 1001

Then we'll assign the number to the phone like this:
ephone 1
button 1:1

The button command assigns the phone button to a DN. Cisco 7960 has 6 buttons which could be assigned numbers. In the example, the first button is assigned to ephone-dn 1. Pressing button 1 would pick up the 1001 line. Notice that a colon is used. There are actually other ways to assign numbers to buttons, like overlaying multiple lines to one number, but we'll do that next time. Right now, we'll stick with this.

Now, set up the other side in a similar fashion and you should end up with two sides. Suppose for the link connecting the two routers, RA has the IP of and RB has the IP of We'll need to find a way to route the calls over. Recall that in our scenario, Site A uses ranges 1001 to 1009, and Site B uses 2001 to 2009. We'll now have to route the calls to each other through dial-peers (exact same one we used in the previous article):
dial-peer voice 1 voip
destination-pattern 200.
session target ipv4:

Do a mirrored configuration for the opposite router and the connectivity would be complete!

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