Information Technology Reference
In-Depth Information
1035. It has also been updated by RFCs 1101, 1122, 1183, 1706, 1876, 1982, 1995, 1996,
2136, 2137, 2181, 2308, 2535, 2782, 2845, 3425 and RFC 3658.
Figure 8-5 shows a simplified view of the DNS process for name resolution. The client de-
vice queries its configured DNS server (the resolver) for the IP address of a fully qualified
domain name (FQDN; for example,
www.cisco.com
). The resolver in turn queries the DNS
server of the foreign or remote DNS server, which responds with the IP address of
www.
cisco.com.
This response is stored in cache on the resolver so that it can be used for fu-
ture queries. The resolver provides the response to the client machine, which can then
communicate via IP address to the destination.
Queries
User quer
y
Internet
Responses
User
response
Local
DNS
Remote
DNS
Server
Client
Figure 8-5
DNS Name Resolution
DNS was implemented to overcome the limitations of managing a single text host table.
Imagine creating and maintaining text files with the names and IP addresses of all the
hosts on the Internet! DNS scales hostname-to-IP address translation by distributing re-
sponsibility for the domain name space. DNS follows a reversed tree structure for domain
name space, as shown in Figure 8-6. IANA
(www.iana.org)
manages the tree's root.
.
(root)
.com
.gov
.net
.org
.edu
.mil
.us
.fr
.de
.mx
.com
.nasdaq
.cisco
.faa .ins
.telmex
.att
.companyx
.hr
.manufacturing
.sales
.marketing
Figure 8-6
DNS Tree
