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.

  • Well the port config screenshot shows interface g1 as being down, so I would look at that first. Start with the physical layer (cabling) and work your way up the OSI layers from there.
    – joeqwerty
    Jan 7, 2013 at 21:41
  • sorry, it's "down" because I need my VoIP system online, so EVERYTHING is plugged into the DELL switch when the screenshots were taken. Jan 7, 2013 at 21:46
  • Currently the dell is directly above the netgear, and when I move the PBX from port 1 (dell) to port 1 (netgear), I lose connectivity. I use the same cabling in both situations. Jan 7, 2013 at 21:47
  • Are you allowing enough time for ARP caches to expire?
    – joeqwerty
    Jan 7, 2013 at 21:50
  • 2
    Are there VLAN's configured that need to be set up on the new switch. I could see that as the cause if everything but the phones are in the default VLAN 1 and the phones are in another VLAN.
    – joeqwerty
    Jan 7, 2013 at 22:30

2 Answers 2


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

  • 1
    Now this is what I would call a crappy factory default - because it simply creates a configuration you never seen with other brands and would never expect in that way. And where there is one, more are to come. Thank you Netgear for providing another vivid example for why not to consider using your products.
    – the-wabbit
    Jan 14, 2013 at 13:53
  • @syneticon-dj I agree. Jan 14, 2013 at 18:28

check if on the netgear you don't have some 802.1q tagging causing packets to go to another vlan. But having a separate VLAN for voip may be a good idea anyway, separating a bit data and voice (think about your VIP's communication sharing the network with every pc/servers in the enterprise...) (you'd need to deploy it across the whole network though...)

  • I'm not well versed in VLAN's, how does it work when the Workstations are connected to the network through the Telephones? Jan 8, 2013 at 16:21
  • There is a good chance that by default they are in separate VLAN. But this changes depending on your phone types (and on their config, usually on the PBX server that send them their config, if they can connect to it). You should ask a local voip person to have a look, difficult remotely ^^ Jan 8, 2013 at 16:25
  • I've looked in the PBX config, and the switch config, and everything is set to use the default VLAN (1). Also, as I specified above, if I plug into a different switch, everything comes online... it's only being blocked when connected to the Netgear switches. Jan 8, 2013 at 16:56

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