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Configuring your network for Hosted VoIP service

Configuring your router

Basic router configuration

The router/gateway is a networking device used to connect your Dthernet local area network (LAN) to an internet service provider (ISP). Below are the requirements for a CPE router when CenturyLink provides the access circuit and when an alternate carrier is used.

  • If RFC 1918 address space is to be used on the IP phones, then the gateway must support network address translation to a globally unique, internet routable IP address: one-to-one (NAT) or one-to-many (PAT).

  • Gateway must support a UDP NAT (PAT) timer value greater than or equal to 60 seconds. All CenturyLink gateways support this.

  • Gateway must not manipulate the SIP packets at the application layer (SIP ALG functionality should be disabled, unless the device is managed by CenturyLink).

  • If your router has an integrated firewall, review this information.

CenturyLink DNS resolvers:


Public SBC IP addresses (IPv4):

  • (Chicago 1)
  • (Chicago 2)
  • (Forest Park)
  • (Highlands Ranch 1)
  • (Highlands Ranch 2)
  • (Los Angeles)
  • (Indianapolis)
  • (Tukwila)

Private SBC IP addresses (IPv4):

  • (Chicago 1)
  • (Chiacgo 2)
  • (Forest Park)
  • (Highlands Ranch 1)
  • (Highlands Ranch 2)
  • (Los Angeles)
  • (Indianapolis)
  • (Tukwila)

If you're using a router that is not managed by CenturyLink, we strongly recommend that you turn off SIP ALG.

Note: WAN bandwidth must be sized to accommodate your data bandwidth plus the total number of simultaneous voice calls (approximately 100Kbps per call with G.711).

Advanced router configuration

DHCP options

For Polycom phones, Cisco MPP, and Cisco SPA122 devices:

Option 160 = ascii

Quality of service (QoS) settings

Router should support a queuing method designed to give all SIP and RTP a higher priority than less critical traffic and ensure that voice packets take precedence over lower priority packets. Specific QoS settings, if needed, should be discussed with your implementation team.

Note: If you're using non-CenturyLink internet access, please obtain required QoS settings from your service provider. CenturyLink is not to modify our managed device configurations (i.e. settings on IP phones). Work with your internet service provider to determine the correct QoS settings to configure your router properly.

IP failover

For information on IP failover, please content your CenturyLink representative.

Configuring your Ethernet switch

Basic Ethernet switch configuration

An Ethernet switch is a computer networking device that connects devices together on a computer network, by using packet switching to receive, process, and forward data to the destination device.

  • We recommend you use an Ethernet switch that supports the VLAN separation of VoIP and data traffic. When using VLAN separation, you should also enable a device-discovery protocol such as CDP or LLDP-MED.

  • We also recommend a power over Ethernet (PoE) switch, but it's not required (POE switch must meet IEEE 802.3af). If you don’t use a PoE switch, you will need to make sure your CenturyLink sales representative knows so that we can include power cords when we ship your phones.

Advanced Ethernet switch configuration

  • 802.1q: all IP phones should be on a separate VLAN. VLAN assignment will be done using link layer discovery protocol (LLDP) or Cisco discovery protocol (CDP) on the router.

  • QoS: LAN should be configured to allow differentiated services code point (DSCP) and CoS values for QoS for voice signaling and real-time protocol (RTP).
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