Switch – What would cause a PBX or SIP phone to not register on the network when using Netgear Switches

dhcpswitchvoip

We have 3 different types of switches in our network.

  1. All of our IP Phones are running on HP 2520-24 PoE switches.
  2. Our primary backbone is "supposed to be" running on Netgear GS748T switches.
  3. Our OLD switches are Dell PowerConnect 2848. These need to be removed.

I've drawn two diagrams (below).

  1. The first one is what we want, but doesn't seem to work.
  2. The second one what we have now, it's working but not desireable.

network layout

My question is quite basic. What is in the Netgear GS748T switches that would

  1. Block my SIP phones from getting IP address when the DHCP server is connected directly to it?
  2. Prevent my PBX from accessing the network?

FYI: If I PING the pbx when it's connected to the DELL server, it responds appropriately, but if I PING it when connected to the Netgear, it times out. The PBX has a static IP set.

All computers (which are on the exact same network) are connected just fine (including receiving IP addresses via DHCP).

Here are some screenshots of the switch config. This is the switch that the VoIP server is connected to.

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The Dell switch is set as unmanaged, and the Netgear connected to the DHCP server is also basically unmanaged (other than having a static IP).

NOTE: we have not configured LAG's (yet) and there is only a single line between switches.
NOTE: the VoIP connection is shown as "offline" because when the screenshot was taken, the PBX was connected to the DELL switch. It shows as "online" when the PBX is connected to the Netgear switch.

Best Answer

Inside the settings of the Netgear switch is a section called Voice VLAN. It defaults to VLAN2 and is Enabled by default.

Now, even though you're not tagging any ports with VLAN2, the switch is still trying to put all voice devices on VLAN2. This is why it's not getting connectivity on voice devices.

When a computer is connected through the phone, the Voice VLAN is still trying to send the phone to VLAN2 while sending the computer to VLAN1.

Disabling the Voice VLAN solves the issue and allows all traffic to function as expected.

Voice VLAN Config

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