VoIP Scenario

juliorcp

Hello Guys!

At first, I would like to thank all of you, I always follow this forum and helped me a lot to get my CCENT. Although not topic for CCNA, I have a big problem with L3 switch and DHCP Server on a router. I can't understand completely the concept of "trunk native" and "access mode".

I have the scenario in attachment and I would like to configure correctly (with voice vlan and data vlan). Anyone can help me in that? Remembering that I just want to understand the concept. For example: which interfaces I need to configure as a trunk (dot1q and others).

I'm from Brazil and I'm studying english too, so... sorry for my bad english!

Thanks!

zrockstar

Trunk ports are used to carry traffic with VLAN tags. End devices have no concept of their VLAN, so access ports are used for end devices as they do not carry tagged traffic. The switch knows what ports belong to which VLAN and as the data comes into the switch from an access port the switch will tag it with the appropriate VLAN and send it through the trunk. Trunk lines are a member of all VLAN unless you specify otherwise, so your trunk lines should be the lines between your switches and routers/L3s. I haven't worked with VOIP or L3 switches, but based off of what I know I believe this to be the same, maybe a pro will chime in and confirm. Your English is great by the way, and welcome to TE!

Legacy User

Which interfaces you want to set to trunk really depends whats being connected to it. If you plan on connecting a pc to the switchport then no need to set it as a trunk port but if you connecting a phone to it then you do. Also, if the pc is connected to the phone and the phone is connected to the switch you need to set it as a trunk port. You have to setup 2 vlans for voice and data.

If you have both dhcps servers running on the router or l3 switch you have to configure router on a switch creating 2 subinterfaces for both vlans to work. On the voice subinterface you just need to add ip helper address which will be the ip of the data subinterface so its knows to give pc's ip address from the data dhcp server.
By typing the cmd on the interface that both the phone and pc connects to

switchport access vlan 50 <--vlan the data packets travels too
switchport trunk encapsulation dot1q <--sets the encapsulation
switchport trunk native vlan 50 <--vlan the data packets travels too
switchport mode trunk <hardcoding interface to trunk
switchport nonegotiate <--turns the interface on to avoid delay in the phone to power on
switchport voice vlan 10 <-- separates the voice packets from data packets 10 is the vlan I placed the phones in

juliorcp

zrockstar and dmarcisco,

Thanks for your attention. This is the first time that I configured IP Phones on packet tracer and I did! But I still have questions about the switchport. I have the scheme below, and it works, but when I put the L2 switch (Fa 0/2-3 - link to pcs and ip phones) into trunk mode, the IP Phones keep working but the pcs don't. Why?

The other question is: when I have DHCP service on L3 switch, the IP Phones don't get IP addresses, why?

However, the lab worked fine! Thanks for your help!

zrockstar

Hard to say, try posting a show run. I have a feeling that you are setting your trunk to only allow the voice VLAN.

juliorcp

@zrockstar,

Here is the lab: https://dl.dropbox.com/s/lamzblfrxeuxad6/TechExams.pkt?dl=1

I still have the same questions (listed above).

- When I put the L2 switch (Fa 0/2-3 - link to pcs and ip phones) into trunk mode, the IP Phones keep working but the pcs don't.
- When I have DHCP service on L3 switch, the IP Phones don't get IP addresses.

Thanks for your help!

xXErebuS

You need to setup an auxiliary VLAN.... Newer switches support Cisco auxiliary be default and all you have to do it
switchport voice vlan XX
switchport access vlan YY where xx is voice vlan and yy is data vlan....

if your working with older equipment or non cisco phones use the following with same variable meanings to setup aux vlans:

switchport trunk native vlan YY
switchport trunk allowed vlan XX,YY
switchport mode trunk
switchport voice vlan XX

You will still need to setup your DHCP options....

xXErebuS

dmarcisco wrote: »

Which interfaces you want to set to trunk really depends whats being connected to it. If you plan on connecting a pc to the switchport then no need to set it as a trunk port but if you connecting a phone to it then you do. Also, if the pc is connected to the phone and the phone is connected to the switch you need to set it as a trunk port. You have to setup 2 vlans for voice and data.

If you have both dhcps servers running on the router or l3 switch you have to configure router on a switch creating 2 subinterfaces for both vlans to work. On the voice subinterface you just need to add ip helper address which will be the ip of the data subinterface so its knows to give pc's ip address from the data dhcp server.
By typing the cmd on the interface that both the phone and pc connects to

switchport access vlan 50 <--vlan the data packets travels too
switchport trunk encapsulation dot1q <--sets the encapsulation
switchport trunk native vlan 50 <--vlan the data packets travels too
switchport mode trunk <hardcoding interface to trunk
switchport nonegotiate <--turns the interface on to avoid delay in the phone to power on
switchport voice vlan 10 <-- separates the voice packets from data packets 10 is the vlan I placed the phones in

These are unnecessary; nonegotiate keeps the interface from doing DTP phase; 2950 doesnt support ISL; access will put it in access mode.

In addition you do not point your IP helper address to the data subnet for the voice subnet....

You simply create two pools on the L3 switch and create the SVI's there for the Vlans.... if the DHCP server is on a different network / subnet then you specify the ip helper address command