3com SuperStack 3 NBX Manual De Usuario

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:

1 In the NBX NetSet - Main Menu window, click System Configuration.

2 Click the System Settings tab and the System-wide button. The System 

Settings dialog box appears.

3 In 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.

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 

, 

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 

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