Couple of basic VTP questions.

Params7

So I just got done reading the VTP chapter in the ICND2 Cisco book twice over now and have two questions:

Q.1 - When configuring a port which connect to a Cisco IP phone, which in turn connects to a desktop - the book says that the following two commands should be configured on that port:

switchport access vlan vlandid
switchport voice vlan vlanid

My question is - Does this put that port in trunking mode even though no "switchport mode trunk" was configured? What would happen if instead of executing those two commands I simply execute the "switchport mode trunk" command?

Q.2 - Regarding VTP updates - Suppose a VTP Client switch has a configuration version which is higher than a VTP server switch. Both have the same domain name, password, the link connecting them is a fully functional trunk. Will the VTP client overwrite VTP server's vlan.dat?

jdballinger

1. It does not put the port in trunking mode. The mode of the port is determined by either switchport mode access or trunk. If it is a trunk port, the access and voice vlan commands are basically ignored. As far as putting the port in trunk mode, consider what is the purpose of a trunk. A trunk is there to carry tagged traffic between two devices, either bridges, switches, or routers (some combination.) If you are putting an access device (phone or PC) on a trunk port, it's not going to get the access to the network that it needs. The frames it is sending down the ethernet cable are untagged, and the switch will treat them as such. Here is the first video from Danscourses on YouTube about VLANs and Trunking. It's pretty good, especially if you don't have access to TrainSignal or CBT Nuggets. http://www.youtube.com/watch?v=aBOzFa6ioLw&feature=share&list=PLB6CB791010430835

If you aren't the YouTube kinda person, then I recommend (actually even if you are, it's still good to use this) using INE's FREE CCNA bootcamp videos for more information. http://www.ine.com/self-paced/ccna/bootcamps.htm

2. The VTP client won't overwrite the servers database. However if the server sees what it views as a more up to date VLAN database, it WILL accept it, even if it's from a client. That's why VTP (version 1 and 2 anyways) is so dangerous in an enterprise environment. Here is a video from TechExam's very own newly-minted CCIE Mrock! http://youtu.be/_h-tDzzky7k

leonlimsg

jdballinger wrote: »

1. It does not put the port in trunking mode. The mode of the port is determined by either switchport mode access or trunk. If it is a trunk port, the access and voice vlan commands are basically ignored. As far as putting the port in trunk mode, consider what is the purpose of a trunk. A trunk is there to carry tagged traffic between two devices, either bridges, switches, or routers (some combination.) If you are putting an access device (phone or PC) on a trunk port, it's not going to get the access to the network that it needs. The frames it is sending down the ethernet cable are untagged, and the switch will treat them as such. Here is the first video from Danscourses on YouTube about VLANs and Trunking. It's pretty good, especially if you don't have access to TrainSignal or CBT Nuggets. VLANs and Trunks for Beginners - Part 1 - YouTube

Hi jdballinger,

My understanding on a trunk port is it will carry VLAN information(tagged traffic) between switches. So why it will ignore the access and vlan commands which stated the vlan id?

Please advise. Thanks (:

FloOz

If you connect a vtp client that has a higher revision number the vlan database of the server will be changed, believe it or not.

FloOz

As for the voice vlan there are different ways of configuring it. The one your describing sounds as if you would want to use a single vlan for data and voice. The config would look something like this.

int fa 0/1
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport trunk allowed vlan 10,20
switchport mode trunk
switchport voice vlan 20

JLAW904

Now I'm confused. The last lab I did configuring a switch--phone--computer setup, I don't remember having to configure it as a trunk (still 2 separate VLANs). I thought it had to be an access port and the phone itself took care of the 802.1q tagging?

Edit: Well, on Cisco's website I came across this:

The switch has two VLANs: one carries data traffic and one carries voice traffic. The switch port can be either access VLAN or trunk VLAN, but you need to configure a voice VLAN to carry the voice traffic.

Configure IOS Catalyst Switches to Connect Cisco IP Phones Configuration Example - Cisco Systems

networker050184

It's confusing the way Cisco handles the configuration, but setting up a voice and data VLAN on a single port is making it a trunk no matter how you go about getting there.

Params7

Thank you for the responses, I'll go through the videos. The way the book (Odom) states it - just executing the switchport access vlan and voice vlan makes the link into a trunk. Also in this example the connection is between the cisco ip phone and the switch, where the cisco ip phone contains a mini-switch (from which another ethernet cable goes to the pc for data vlan) - so technically it is a connection between two switches which carry traffic for two vlans (a data access and voice) so I guess that makes it a trunk.

again i'm not sure why just executing switchport mode trunk on the interface won't work for this purpose also..maybe it won't just be limited to just those specific voice and data vlans but to my understanding it should start tagging frames to the switch in the cisco ip phone and vice versa.