DNS Lookups & Performance Monitoring

DNS Lookups & Performance Monitoring A DNS Lookup is when a device that supports IP asks a DNS server for the IP address associated with a domain name. The DNS Server must “look up” the IP associated with that domain name.  A DNS lookup uses an Internet domain name to find an IP address, where a reverse DNS lookup is using an Internet IP address to find a domain name. Reverse DNS lookup technique is able to identify if the sending e-mail server is legitimate and has a valid host name.

EXAMPLE : If you were to go to KRISARU.com in your browser, your computer would initiate a DNS Lookup. This process involves asking the Primary DNS Server for KRISARU.com’s IP address. The DNS Server will ask other servers until the IP address is found and the information returned to you.

A common analogy is that DNS is like a very large phonebook. You look through the phonebook for the name you want and it will tell you the number you need to dial the person you’re looking for. The process of looking up the number is a “DNS Lookup”.

If you would like to experiment with DNS Lookups, you can use the command line utility “nslookup” in Windows or Linux.

This method tries to eliminate spam sent by e-mail servers connected through Internet dial-up connections, as well as most ADSL and cable connections. IP addresses of those connections are usually not registered to any DNS as a qualified host meaning that they do not have their own static IP and a registered host name like mail.domain.com.

Many spammers use misconfigured hosts to disguise the source of the spam. A DNS query that does not recover a matching host name and IP address is a good indication that the message is spam.

DNS lookup is not always a good solution. Many legitimate e-mail servers are incorrectly configured, or have intentionally not registered a name with DNS, so a reverse query does not return a matching host name. Also, this anti-spam method runs DNS queries on a large number or e-mails and consumes valuable network resources. A number of problems, including network delays and improperly configured networks or servers, can prevent legitimate messages from getting through the filter. In January 2003, AT&T WorldNet started using reverse DNS and was forced to remove the filter just 24 hours after it was deployed, after subscribers reported that messages were going undelivered. Read more……

Resource Links :

  • DNS Watch – DNS Lookups & Performance Monitoring
  • DNSstuff – DNS Management Tools
  • Hostingfacts – Free & Paid website monitoring tools/services