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L2 traffic between VLANs

Hello guys,

I will be short with this question. I have some IP phones in my network, and servers supporting them. So far, they have been in a same subnet, but now when we implemented VLANs, I realized how stupid technology we have in our network. We have IP phones that don`t do IP. They use multicast instead.

So, now when they are in different VLANs, phones and servers can not communicate? Is there some way of enabling L2 access and broadcast from one VLAN to another? Or maybe configuring switch port for phones to be a member of two VLANs at a same time?

Any suggestion in welcome. Thank you in advance.

Peter Paluch
Hall of Fame Cisco Employee


Can you be more specific about your VoIP technology? I somehow do not understand how your phones actually work with the "multicasts" I guess that understanding your technology in more detail could help to solve your problem.

In any case, if your "IP" phones use IP multicasts then IP multicast routing could be configured between your VLANs. If they do not use any routed protocol to communicate and encapsulate the voice data into Ethernet frames directly then I guess we're out of luck.

Understanding your technology would definitely help here.

Best regards,


Hello Peter, thank you for your quick response. I do not have documentation next to me, but will look through it tomorrow, and post my finding here. Im dealing with 3com phones, and my guess is that they use MAC addresses to "find" servers, or initial broadcast before they switch to unicast traffic. Anyway, they can not find servers from different subnet. Not sure yet, I`ll check the documentation and report here.

Thanks for replying once again!