Known Issues

  1. CDP (Cisco Discovery Protocol) needs to be disabled if you are not using it to prevent it from autoconfiguring the phones on a separate VLAN from the computers.
  2. These devices also may have an Auto Voice VLAN setting that will need to be disabled if it's not being used.
  3. DNS relay/proxy needs to be disabled if enabled to prevent intermittent DNS lookup timeouts on just Polycom phones.


  1. Intermedia technicians cannot make the changes described below for you.  Cisco managed switches usually don't have a web interface.  They usually require either plugging a computer into the Console port on the back on the switch or connecting to the switch using a remote administration service, like Telnet, if enabled.
  2. Your IT or a Cisco technician will need to add the following line to your switch's configuration file if you are not using CDP:
    • no cdp
      • The no CDP setting above prevents the switch from automatically putting the phones on a separate Voice VLAN. 
      • Some new Cisco switches also have a separate setting called Auto Voice VLAN that needs to be disabled. 
      • The phones either need to be on the same subnet as the computers or on a separate subnet with their own compatible router.
  3. If you have or plan to purchase Polycom phones, the DHCP server on the network needs to instruct the phones to use efficient DNS servers, like Google's or OpenDNS, as their Primary and Secondary DNS servers.  
    • This is because many ISP DNS servers take too long to relay the Polycom phones' DNS lookup requests, which causes the phones to intermittently lose registration.
  4. DNS proxy/relay needs to be disabled on the switch if enabled, so that the phones are told to use the efficient DNS servers instead of sending their DNS requests to the switch or another local DNS server to then have the requests relayed to outside DNS servers. 
    • This reduces the time it takes for the phones to resolve domain names, which ensures the phones stay registered with our servers.
  5. As long as all outbound traffic from just the phones is allowed, which it is by default on these Cisco devices, then creating access rules (ACLs) for the phones is usually unnecessary.
  6. Port security can be setup on these Cisco devices to not allow a phone to use specific Ethernet ports on the ASA unless your IT or a Cisco technician adds the phone's MAC address to a trusted list. 
    • If one or all of your phones cannot get an IP address  they say Network is down or Configuring, then you will need to contact your IT or a Cisco technician.