DNS解析：域名系统详解

A perpetual stumbling block in understanding the DNS is how pointer queries as handled - Given an IP address , return the name corresponding to the address

When an IP datagram arrives at a host for a server, be it a UDP datagram or a TCP connection request segment , all that's available to the server process is the client's IP address and port number (UDP or TCP)

We've seen a few different types of resource records so far an IP address has a type of A, and PTR means a pointer query .

To reduce the DNS traffic on the Internet , all name servers employ a cache. With the standard Unix implementation , the cache is maintained in the server, not the resolver.

We've manetioned that the well-known port numbers for DNS name servers are UDP port 53 and TCP port 53.This implies that the DNS supports both UDP and TCP.

The domain name system , or DNS , is a distributed database that is used by TCP/IP applications to map between hostnames and IP addresses, and to provide electronic mail routing information.

The DNS name sapce is hierarchical, similar to the Unix filesystem.

There is one DNS message defined for both queries and responses.

Question Portion of DNS Query Message

Resource Record Portion of DNS Response Message