NSLookup

nslookup is very good to trouble shoot LAN/WAN problem...



http://technet.microsoft.com/en-us/library/aa997324(EXCHG.65,loband).aspx

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For Exchange Server to send Internet mail, the DNS servers that Exchange Server uses for your domain must be able to resolve external domain names. To verify that your DNS servers can resolve external domain names, use the Nslookup tool (Nslookup.exe) if you are running Exchange 2003 on Windows 2000 servers.

Before You Begin

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Before you perform the procedure in this topic, read Verifying DNS Design and Configuration .

Procedure

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How to use Nslookup to verify DNS configuration

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At a command prompt, type Nslookup, and then press ENTER.

Type server , where IP address is the IP address of your external DNS server.

Type set q=MX, and then press ENTER.

Type , where domain name is the name of an external mail domain, and then press ENTER. The mail exchanger (MX) resource record for the domain that you entered should be displayed. If the MX record is not displayed, DNS is not configured to resolve external domain names.

Example

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The following example shows how the DNS server for example.com resolves the IP address of the external domain contoso.com:

C:\> nslookup

Default Server: pdc.corp.example.com

Address: 192.168.6.13

> server 10.255.255.255

Default Server: dns1.example.com

Address: 10.255.255.255

> set q=mx

> contoso.com.

Server: dns1.example.com

Address: 192.168.10.10

contoso.com MX preference = 10, mail exchanger = mail1.contoso.com

contoso.com MX preference = 10, mail exchanger = mail2.contoso.com

contoso.com MX preference = 10, mail exchanger = mail3.contoso.com

mail1.contoso.com internet address = 192.168.255.011

mail2.contoso.com internet address = 192.168.255.012

mail3.contoso.com internet address = 192.168.255.013

In this example, the preconfigured DNS server is behind a proxy server. Therefore, an external or Internet DNS server with a known IP address of 10.255.255.255 was used to perform the query. Next, the query type was set to MX to locate the mail exchangers for contoso.com. In this example, three SMTP servers are equally balanced, each with its own IP address.