VoIP Phones/VLAN-DHCP

[j_finley]

I have PC's connected to VoIP phones where it is in connected to the switch. I believe I have all the ports configured correctly however, my VoIP phones on VLAN20 for instance cannot retrieve an IP from our DHCP server. The DHCP server is configured w/ two scopes. My phones end up getting an IP from VLAN1 (Data VLAN) instead. If I staticly set the phones, they communicate fine. Any idea why this is happening? Note: I have a 3640 router w/ 2 FE's. One for the Data VLAN and the other for Voice VLAN with the ip helper address on the voice vlan interface.

[amitsin]

Which switch you are using ?

Could you please paste the config from the switch and the router.

I guess your router is acting as a DHCP server. Can you please more elaborate on the topolgy connections.

[j_finley]

Actually, I have a Windows 2000 box as DHCP server.

All switch ports are configed like:

----------------

interface FastEthernet0/1

description phone and PC

switchport trunk encapsulation dot1q

switchport mode trunk

switchport voice vlan 20

no ip address

duplex full

speed 100

spanning-tree portfast

!

interface FastEthernet0/2

description phone and PC

switchport trunk encapsulation dot1q

switchport mode trunk

switchport voice vlan 20

no ip address

duplex full

speed 100

spanning-tree portfast

!

-----------------------------------

I have a 3640 router w/ 2 FE's plugged into a 3550 and 4003 switch. The 3550 interface w/ the router plugged in is follows:

----------------------

interface FastEthernet0/47

description CONNECTED TO ROUTER FE0/1

switchport access vlan 20

switchport mode dynamic desirable

-----------------------

The Cisco 4003 switch has the other router connection:

-----------------

! Router connected FE1/1

set trunk 3/2 on dot1q 1-1005

[amitsin]

Please change the port configs to the following :

nterface FastEthernet0/1

description phone and PC

switchport access vlan 1 ----> Data vlan

switchport voice vlan 20 ----> Voice vlan

no ip address

duplex full

speed 100

spanning-tree portfast

The reason is, when we connect the IP phone to the switchport on 3550's it forms a special dot1q trunk to carry both the data and the voice vlan only. This is the suggested configuration on the 3550 ports however on 3500 Xl switches your configuration is the suggested one.

Make sure that you set the ip helper-address command on the appropriate vlan interfaces.

HTH

Amit Singh

[j_finley]

Well, that's my main question. Do I create VLAN interfaces and assign it an IP even though I have a router doing the routing? In my one book (Cisco Catalyst LAN Switching), it suggests three types of routing, one using a router, the other creating VLAN interfaces in place of the router IP and routing it that way. I guess I'm just really confused. Does my router have to be used or will the switch do it? The 4003 switch only has a L2 Sup. 1

My router is configured as FE 0/1 192.168.10.1 (data)

FE 1/1 192.168.20.1 (voice), what would the IP for the VLAN interfaces be?

[amitsin]

Where is DHCP server connected. How is your 3550 connected to the router and howz 4003 is connected to the router.

Can you send me a brief topolgy, sh run from 3550, sh run from router at ( amitsin@cisco.com )

Once I have the topolgy, I would be in a better position to assist you.

[j_finley]

Amit,

What about my CATOS config for the port? I have port 3/18 for instance set as the following:

set port auxiliaryvlan 3/18 20

!

set trunk 3/18 on dot1q 1-1005

set trunk 3/19 on dot1q 1-1005

!

And that's pretty much it. As that all I have to do for my CatOS switch(4003)?

Also, did you get a chance to look at my email directed to you with attachements?

Joe

[amitsin]

Joe,

I didnt get your mail. Please forward me again at amitsin@cisco.com

[erfreeman]

are you using a cisco switch? if you are you need to have the voice vlan or auxilary vlan set on the switch.

confirm that you can ping the dhcp server and the call manager from the voice vlan

also you need to have dhcp options for your dhcp scope.

you should have dhcp option 150 in your dhcp scope

option 150 is your tftp server typically your call maanger.

this is my setup with all cisco gear

[j_finley]

I don't have call manager, we're using ShoreTel; however, I can ping dhcp server from the voicemail server on the other subnet. When I do a traceroute, it confirms two hops.

Also, I do have aux lan set on my CATOS switch which is considered our core and all my 3550's GBIC to it.

[dabels]

Aux vlan should only be configured on a CATOS port that is going to have a telephony device plugged into it it will not help if it is just a transit port

between two switches or a router, you will have to devine trunks for that. if you plug a pc into the phone does it work correctly? you get the right lan on the pc?

regards,

Dave

[erfreeman]

here is the output of one of my interfaces. vlan 11 data. vlan9 voice.

I think the issue sounds like a dhcp issue where the phone is not getting the correct subnet information. With the Cisco phone you need to use option 150 which is a tftp server. And the tftp server is the Cisco Call Manager. Then the phone gets the appropriate DHCP scope. I am not sure if you have this or not but you need an ip helper command to allow the dhcp requests to travel between vlans. You set that up on the router.

interface FastEthernet2/12

switchport access vlan 11

switchport mode access

switchport nonegotiate

switchport voice vlan 9

spanning-tree portfast

[j_finley]

Do I need the router FastE's to be plugged into the same switch? or can they be on separate switches? I have the IP helper command on the voice vlan port of the router.

Also, do I need to create VLAN interfaces for each VLAN and assign them an IP? I just don't understand the point if I have a router doing the routing. Can someone explain why they would create a VLAN interface and assign an IP to it? Sorry, I have about 3 VLAN books and none of them answer that basic question.

[j_finley]

Ok, I have every port set to AUX Vlan, even ports with a server plugged into it. I don't notice any problems though?! All my configs till now are coming from a book "Cisco Catalyst LAN Switching" from McGraw Hill. It seems a bit dated as I've been corrected a few times which I'm greatful for.