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3750 Catalyst Switch config issue - VoIP phones hopping vlans

Posted on 2008-10-31
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Last Modified: 2008-10-31
Our network has 2 vlans one for voice which points to a router connected to a T1 for voice and the other for data connected to a router with a T1 for data. This has worked fine with a couple 24 port 2950's.

We just installed a new switch. Now some phones work perfectly while others are getting their IP address from our DHCP server on the data vlan rather than our voip providers dhcp server.

The phones are Cisco 7940's. The only thing that changed on the network was everything was unplugged from the old switch and connected to the new switch.

The switch is 48 ports. In the attached config I removed ports 2-48 as they are all configured identically.

Is there anything obvious here that could be causing this? Any help would be immensely appreciated!


Building configuration...
 

Current configuration : 9739 bytes

!

version 12.2

no service pad

service timestamps debug uptime

service timestamps log uptime

service password-encryption

!

hostname IT1Source3750

!

enable password 7 ####

!

no aaa new-model

clock timezone MST -7

switch 1 provision ws-c3750g-48ps

system mtu routing 1500

ip subnet-zero

no ip source-route

no ip domain-lookup

!

!

!

!

no file verify auto

!

spanning-tree mode pvst

no spanning-tree optimize bpdu transmission

spanning-tree extend system-id

no spanning-tree vlan 1-4

!

vlan internal allocation policy ascending

!

interface GigabitEthernet1/0/1

 switchport trunk encapsulation dot1q

 switchport mode trunk

 switchport voice vlan 2

 switchport priority extend cos 3

 spanning-tree portfast
 

!

interface Vlan1

 description LAN Data VLAN (Inside/Private/Default VLAN)

 ip address 10.0.1.252 255.255.255.0

 no ip route-cache

!

interface Vlan2

 description Voice Vlan

 no ip address

 no ip route-cache

 no shutdown

!

interface Vlan3

 description Mgt Vlan

 no ip address

 no ip route-cache

 shutdown

!

ip default-gateway 10.0.1.254

ip classless

no ip http server

!

!

control-plane

!

!

line con 0

 password 7 ####

 login

 stopbits 1

line vty 0 4

 password 7 ####

 login

line vty 5 15

 login

!

end

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Question by:xy8088
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3 Comments
 
LVL 15

Expert Comment

by:bkepford
ID: 22850644
If you are using all Cisco phones confiure your ports like this
interface GigabitEthernet1/0/1
switchport mode access
switchport access vlan 1
switchport voice vlan 2
switchport priority extend cos 3
spanning-tree portfast

Cisco phone will use CDP to detect the voice VLAN and even though your not running dot1q per say it should work just fine.
 
 
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LVL 3

Author Comment

by:xy8088
ID: 22850859
So I just go in to configure that interface and issue the command:
switchport mode access

Will that also remove the:
 switchport trunk encapsulation dot1q

Or is that a separate command? Sorry for my ignorance, all our Cisco guys are gone and I'm on my own for this.
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LVL 15

Accepted Solution

by:
bkepford earned 495 total points
ID: 22850905
interface range GigabitEthernet1/0/1-48
no switchport mode trunk
no switchport Trunk encap dot1q
switchport mode access
switchport access vlan 1



 
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