"switchport voice vlan xxx" - strange behavior on C3750 stack

Unanswered Question
Sep 1st, 2010

Hello!

I have one stack made of 2 x C3750 and access port configuration looks like this on all access ports:

switchport access vlan 10
switchport mode access
switchport nonegotiate
switchport voice vlan 666
no logging event link-status
no logging event power-inline-status
no snmp trap link-status
no cdp enable
spanning-tree portfast
spanning-tree bpduguard enable

Now, vlan 10 is the data vlan, and vlan 666 is the voice one...you probably understood this already.

Then I have the following configuration:

stack (one of this 2 switches) -> IP phone -> PC

On one of the switches is working fine, on the other one not:


WORKING:

sh mac address-table int fa2/0/6
          Mac Address  Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------        --------    -----
  10    0013.728d.435a    DYNAMIC     Fa2/0/6
666     0001.e32c.7297    DYNAMIC     Fa2/0/6

NOT WORKING:

sh mac address-table int fa1/0/14
          Mac Address  Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------        --------    -----
  10    0001.e32c.7266    DYNAMIC     Fa1/0/14
  10     0019.bb58.0189    DYNAMIC     Fa1/0/14

So, the same IP Phone + switch works fine on every port in the switch 2 in the stack, but not in switch 1 on the same stack.

You see that on the 1st switch, both devices are taking the same VLAN 10. Mac-addresses starting with 0001 are the IP Phones.

Before asking about power inline:

sh power inline fa1/0/14
Interface Admin  Oper       Power   Device              Class Max
                            (Watts)                           
--------- ------ ---------- ------- ------------------- ----- ----
Fa1/0/14  auto   on         7.0     Ieee PD             2     15.4

Interface  AdminPowerMax   AdminConsumption   
             (Watts)           (Watts)          
---------- --------------- --------------------

Fa1/0/14              15.4                 15.4


sh power inline fa2/0/6
Interface Admin  Oper       Power   Device              Class Max
                            (Watts)                           
--------- ------ ---------- ------- ------------------- ----- ----
Fa2/0/6   auto   on         7.0     Ieee PD             2     15.4

Interface  AdminPowerMax   AdminConsumption   
             (Watts)           (Watts)          
---------- --------------- --------------------

Fa2/0/6               15.4                 15.4

Some more details:

sh int fa1/0/14 switchport
Name: Fa1/0/14
Switchport: Enabled
Administrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 10 (CLIENT)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: 666 (VOIP)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none

sh int fa2/0/6 switchport
Name: Fa2/0/6
Switchport: Enabled
Administrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 10 (CLIENT)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: 666 (VOIP)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none

Is there something so obvious that I don't see, or the first C3750 in stack is going crazy?

Thanks!

I have this problem too.
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Calin Chiorean Wed, 09/01/2010 - 03:22

OK, I have found the solution!

Actually it wasn't related to the switch port / network configuration. Maybe and important fact that I forgot to mention is that the IP phone and the PC client are getting IP addresses through DHCP. Guess what? The scope was full in the client range.

That was the problem!

Thanks all who had a look into this issue!

P.S. If some forum admin can mark this question as solved, it will be great. I cannot do it for my own reply!

Giuseppe Larosa Wed, 09/01/2010 - 05:20

Hello Calin,

don't worry about the solved flag you have found yourself  the root cause of your issue and you have been kind to provide it.

Best Regards

Giuseppe

Calin Chiorean Wed, 09/01/2010 - 05:58

Thank you for these kind words!

I usually try to provide the solutions if I found them, because I know from own experience what pain can it be when you do a search, find the topic of your interest, but no solution.

Cheers,

Calin

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