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VOIP port switch 3750

dear all,

i have problem in my cisco 3750

  • when i tagged ports the avaya phone works

  • but when i add ports in vlan voice directly the phone not worked

please help me, an thank you. GSM. (00 216) 93 124 999/ 22 741 725

VOIP port switch 3750


Voice vlan is special feature.

Voice Vlan.

Whenever a phone is connected to the switch port,switch exchange information with phone with vlan address and TFTP address.then switch guides the phone with vlan path,gateway and tftp address.

In your first configuration,you are using voice vlan command and information will be exchanged.

you can connect both phone and host,both will work.

Another thing,because of voice vlan command,host will be getting data vlan ip and phone will be getting Voice vlan Ip

In your second config,your staticly assigining vlan,it will work like regular vlan and phone cannot communicate to tftp server and call manager.


VOIP port switch 3750

but vlan 18 is for voip

all telephony sytem connected on this vlan
GSM. (00 216) 93 124 999/ 22 741 725 GSM. (00 216) 93 124 999/ 22 741 725

VOIP port switch 3750


Eventhrough Its voice vlan only,the packet will be tagged has vlan 18.

When Voice VLAN feature enables access ports to carry IP voice traffic from an IP phone. When the switch

is connected to a IP Phone, the phone sends voice traffic with Layer 3 IP precedence and

Layer 2 class of service (CoS) values, which are both set to 5 by default.

VIP Expert

Re: VOIP port switch 3750


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Guru has already answered what's different, but to clarify, an Avaya phone can work on tagged or non-tagged VLANs.  When working with tagged frames, it needs to know what the expected tag will be.

When you connect your Avaya phone to your first port configuration, and it works, it then expects VoIP traffic to be tagged with VLAN 18.  If frames are not so tagged, it will ignore the frame (which is why it will ignore the non-tagged port data traffic on VLAN 16).

If you connect the same Avaya phone to your second port configuration, the Avaya phone will still ignore the non-tagged frames, even though they are VoIP frames.  I.e. your Avaya phone's configuration needs to be changed to accept VoIP frames as non-tagged.

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