Overview of Virtual Tie Lines 77
Configuring Domain
Name Server
Information
When the SMTP utility attempts to send e-mail, it must be able to resolve
a host name within an e-mail address and determine the proper IP
address from that name. Domain Name Servers on the Internet perform
this function. You can configure up to three DNS entries with the NBX
NetSet utility. The NBX system uses the second and third entries if the first
or second cannot be reached. To configure DNS information in the NBX
NetSet utility:
1In the NBX NetSet - Main Menu window, click System Configuration.
2Click the System Settings tab and the System-wide button. The System
Settings dialog box appears.
3In the Primary DNS, Secondary DNS, and Tertiary DNS text boxes, type the
IP addresses of three Domain Name Servers. If you have the IP address of
only one server, type it in the Primary DNS text box. If you have the IP
address of only two servers, type them in the Primary and Secondary DNS
text boxes. Click OK.
Overview of Virtual Tie Lines
A Virtual Tie Line (VTL) provides a way to make calls between NBX system
sites that are separated geographically but tied together by a Wide Area
Network (WAN) connection. An NBX 100 system can support up to 8
simultaneous VTL connections; a SuperStack 3 NBX system can support
up to 48. VTLs are a licensed feature of the NBX systems.
On any NBX system, any licensed VTL connection can be used either for
an incoming VTL call from any site or for an outgoing VTL call to any site.
A VTL connection is not dedicated in the same way as a physical tie line,
which always connects the same pair of sites. In the example in Figure 8,
the VTLs on the Chicago NBX system can be used for any combination of
incoming and outgoing VTL calls to either Atlanta or Dallas.
The NBX system can reroute VTL calls that fail to reach their destination
on the first attempt. For details, see “Call Rerouting for Virtual Tie Lines”
on page 90.
■You must implement either IP On-the-Fly or Standard IP on an NBX
system in order to use VTL connections to other NBX systems.
■VTL connections cannot be configured to run through firewalls or NAT
routers.
■When you calculate the number of devices on an NBX system, do not
include the number of VTLs.