Internet Protocols - CCIE Routing and Switching Exam Certification Guide - page 296

DNS

DNS is a method to manage Internet names in a distributed fashion. DNS servers return the
destination IP addresses given the domain name. DNS was first specified by RFCs 882 and 883.
The current specifications are RFCs 1034 and 1035.

DNS is a distributed database, where separate organizations administer domain name space and
can then break the domain into several subdomains. DNS follows a reversed-tree structure for
domain name space. The Internet Name Registration Authority manages the root of the tree.
The DNS tree is shown in Figure 6-14.

DNS Tree

Figure 6-14

.(root)

.com .gov .net .org .edu .mil .us .fr .de .mx

.com

.nasdaq .cisco .faa .ins

.telmex .att

.companyx

.hr .manufacturing .sales .marketing

DNS uses TCP and UDP port 53. UDP is the recommended transport protocol for DNS queries.
TCP is the recommended protocol for zone transfers between DNS servers. A DNS query
searches for the IP address of a Fully Qualified Domain Name (FQDN), such as www.cisco.com.

SNMP

SNMP is a network protocol for the management of network devices. SNMP allows network
managers to inspect or change parameters on a device remotely. SNMP was first defined by
RFC 1067 (SNMPv1), which was succeeded by RFCs 1155, 1157, and 1212. Version 2 of
SNMP is defined by RFC 1442, with other RFCs providing updates. The latest version of
SNMP, version 3, is described in RFC 2573.

In SNMP, managed devices (routers, switches, servers) contain an SNMP agent. The agents
collect and store management information. The information is made available to the network
management system (NMS). NMS uses read and write commands to query or change information