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Rolling out UC500 into flat LAN


how hard is it to roll out a UC without using a dedicated voice VLAN?  For example, onto a site where end-to-end VLANs don't work?

The mix of switches, lack of CDP and small number of handsets means that we would like to roll out to a flat LAN - no dedicated voice VLAN, no VLAN-based QoS etc.  Run it all untagged, in a total-loss non-design as it were.

What are the main steps to get the UC500 to work in this situation?

Go into VLAN.DAT on the UC and delete all VLANs except VLAN1? Run the UC as a DHCP server on this VLAN, which runs over the local LAN untagged, or let the phones get IP addresses from a Windows server DHCP scope, with an option 66 or 150 to point them to their TFTP server/CME?

Is it as simple as that, or am I missing something extra/obvious/big?

Thank you.

paolo bevilacqua
Hall of Fame Master

It is not a matter of how hard it is, rather of how bad it is.

Flat VLAN - inadequate switches - typical chaotic small business setup = a lot more work and uncertaints = big risk for IP telephony to work poorly or be affected by other traffic.

Sure you will come back, and say "that's my customer situation, he wants like that, I can't change it".

Fine, but remember, if you accept that, you will also have to accept your customer blaming you for voice not working good, or even data, since you introduced voice on the same LAN, and "everything was working before".

There is a reason -beyond technicality- why "best practices" are published and why certain recommendations are routinely made: to guarantee your success and profitability.

Think about it before you start doing things a different way.

Please consider what Paolo said because he is pointing out very important points.

If you still want to run a setup like that, go with a single DHCP server for everything. And since I suppose you have Active Directory and DNS in there, go with the Windows DHCP and not the UC DHCP server.

We ran into an issue where VLANs were improperly configured once, and there was a Windows DHCP server servicing computers and UC DHCP for the phones, and for some reason, some phones would get an IP from the Windows DHCP server and not communicate with the UC...

Hello Paolo and MDube,

thank you for your answers - from a design point of view I agree with you both.

As is fairly common in a SMB environment, I am maintaining a system/network with no budget for upgrades, no smartnet support and with a network built from second-user parts - 'just make it work'. 

I feel a bit like a cook on a pirate ship.

In the customer's defence, the IP phone system has been running ok in a single VLAN for several years to date, but hasn't been patched or updated since 2005, which I have managed to do.

I need to get it all back onto one VLAN rather than the default data and voice VLAN setup - the 2x VLANs work ok from the face of the UC, but can't be done end-to-end throughout the LAN.

We do have AD and a windows-based DHCP server and could use that.

Is it really as simple as deleting extra vlans in VLAN.DAT and then setting options in the Windows DHCP scope?

Thank you again.