Wednesday, October 7, 2015

DNS Resolution Process

Domain Name System (DNS)
DNS resolves host names to IP addresses. This eliminates the need for you and me to have to remember the IP address for web sites. Instead, we simply type the name into the browser, and it connects. For example, if you type in as the Uniform Resource Locator (URL) in your web browser, your system queries a DNS server for the IP address. DNS responds with the correct IP address and your system connects to the web site using the IP address.

DNS also provides reverse lookups. In a reverse lookup, a client sends an IP address to a DNS
server with a request to resolve it to a name. Some applications use this as a rudimentary security mechanism to detect spoofing. For example, an attacker may try to spoof the computer’s identity by using a different name during a session. However, the Transmission Control Protocol/Internet Protocol (TCP/IP) packets in the session include the IP address of the masquerading system and a reverse lookup shows the system’s actual name. If the names are different, it shows suspicious activity. Reverse lookups are not 100 percent reliable because reverse lookup records are optional on DNS servers. However, they are useful when they’re available.

Two attacks against DNS services are DNS poisoning and pharming.

DNS Resolution Process
1 - Request sent to local name server
2 - Name server queries root server
3 - Root response sent to local name server
4 - Name server queries .com name server
5 - .com Response sent to local name server
6 - Name server queries specific domain server
7 - Domain server responds to name server
8 - Name server provides result to local device
9 - Answer is cached locally

DNS Records
• A and AAAA - Address
• CNAME - Canonical name
• MX - Mail exchanger
• NS - Name server
• PTR - Pointer

Source Processor Messer

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