DHCP and ip assignment with VoiP

Logman asked:

We just added a Cisco SPA122 ATA with Router to our network, it will be used for our paging system (an amplifier/speakers). We are having a hard time getting it work. Well until we found out the ip that the Cisco SPA was using was also using the same ip as one of our servers.

Now, is this something that can be fixed via our DHCP server?
Or is this a problem with the Cisco SPA? It is a router with DHCP server/client. Would this be considered a rogue dhcp server? And could this cause more problems for our network?
Our network uses 192.168.1.x btw

My answer:

The Linksys SPA122 that you purchased includes a very small two-interface SOHO router, as it was designed to sit at the edge of the internal network and do traffic shaping to improve voice quality. In its intended configuration it connects directly to your cable/DSL modem via the “Internet” port, while your internal LAN connects solely to its “Ethernet” port.

It’s expected that you would connect to the device (via its Ethernet port) and reconfigure it to meet your local needs in this scenario. And if you intend to use it as an end device rather than in the configuration it was designed for, you’ll have to do so in order to configure it to use some other (unused on your network) IP address range. The reason for this is that both interfaces can’t be on the same subnet.

So you can reconfigure the device, (note that you can only do this from the Ethernet interface) just changing the IP address range it thinks it controls to an RFC1918 range that isn’t used in your network, or send it back and get an SPA112, which is otherwise identical except that it does not have a built-in router.

View the full question and answer on Server Fault.

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