Known Issues

  1. SIP ALG is enabled by default and most firmware versions in these routers have no option to disable it.
  2. MTU is set to Auto by default, which can set it to 576, which is too low.  
    It causes intermittent phone feature failures & audio to cut out mid-calls.
  3. The firmware on this series of routers are very buggy, but Cisco has worked hard to resolve most of the VoIP-related problems in their 2014 firmware releases.  It's critical to upgrade these routers to the latest firmware version to avoid strange call audio and phone registration issues.
  4. There is no option to change the router's UDP session time out value which causes intermittent registration failures on Polycom phones due to the fact that the router is blocking the phones' NAT Binding/Keep-Alive packets that are sent every 15 seconds. This problem persists even after upgrading to the most recent firmware version ( as of 3/7/17).

Temporary Resolution

  1. The steps below may vary slightly due to the wide range of models and firmwares in the RV-series. 
    • Contact your IT or Cisco if you're unable to find the settings listed below.
  2. Log into the router.
  3. Change the MTU from Auto to one of the options below.  
    • This setting is usually found under Setup > Network > WAN.
      Your router may reference 'WAN' as Internet Settings or with slightly different terminology, depending on the model and firmware:
      • 1500 for Cable
      • 1492 for DSL
      • FiOS using PPPoE (most pre-2006 FiOS circuits) – 1492
      • FiOS using DHCP (most post-2006 FiOS circuits) -- 1500
      • Contact your ISP if you're unsure.
  4. This step is only needed if you have or plan to purchase Polycom phones:
    • If you are using the router as the DHCP server, go to Networking > LAN > IPv4 LAN
      Set the following:
      • Primary DNS Server -
      • Secondary DNS Server -
      • Uncheck DNS Proxy
      • Click Save.
  5. This optional step is needed for call quality monitoring and troubleshooting purposes.
    • Go to Firewall -> Attack Protection -> Enable Respond to Ping on WAN (Internet)
    • Restrict Web Features (Web Filter):
      • Java: Unchecked - this is needed for the Intermedia voicemail player and other online tools
    • Click Save
    • All other firewall settings on this page do not affect the phones.  
      • Below are the recommended settings for optimal network security and to allow Intermedia web-based tools to run.  However, your IT may want these settings configured differently:
        • Firewall: Enable
        • SPI (Stateful Packet Inspection): Enable
        • DoS (Denial of Service): Enable
        • Remote Management: This is okay to have enabled or disabled.  If enabled, make sure you have a strong router password.
        • HTTPS: This is recommended but not required for more secure remote management.
        • Multicast Passtrhough: Enable
        • Restrict Web Features (Web Filter):
          • Java: Unchecked/Not-Blocked - this is needed for the Intermedia voicemail player and other online tools
          • Cookies: Unchecked/Not-Blocked - this is needed for Intermedia websites
          • ActiveX: Unchecked is recommended to allow many web-based apps to run in Internet Explorer.  However it can be checked to prevent users from running malicious web apps.
          • Access to HTTP Proxy Servers: This can be unchecked or checked.
  6. Check to see if the router has an option to disable SIP ALG.
    • This is usually found under Firewall -> Advanced Setting > Disable SIP ALG > Save
    • If there isn't an option to disable SIP ALG, you or your IT will need to upgrade the router to the latest firmware version.  If you need help, call Cisco.
    • If the router is running the latest firmware and it still doesn't have the option to disable SIP ALG, then you will need to replace the router with a recommended or serviceable one.
  7. Upgrade the router to the latest firmware version - if you did not already in step 6.  
    • Back your current router configuration first.
    • This is needed to resolve many intermittent call audio and registration-related problems that affect many models and firmware versions in the RV-series.
    • Intermedia cannot do this for you, but your IT can, or you can call Cisco and they can help guide you through the process.

Permanent Resolution

  1. Buy a Recommended Router if you do not have one already. The list of recommended devices can be found here.
    • Intermedia cannot setup the new router for you, but your IT or the manufacturer of your new router can help you. 
    • They will need to move settings from the old to the new router to ensure your computers and other devices on the network work properly.