Infrastructure Services: DNS, DHCP, NTP, HSRP

This chapter is from the book

CCNA Routing and Switching 200-125 Exam Cram, 5th Edition

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This chapter is from the book

This chapter is from the book 

CCNA Routing and Switching 200-125 Exam Cram, 5th Edition

Learn More Buy

This chapter ensures you are ready for the preceding topics from the Infrastructure Services section of the overall exam blueprint from Cisco Systems. Remember, this is just a section of the Infrastructure Services area. Chapter Fifteen, which deals with NAT, also exists in this grouping.

Essential Terms and Components

• DNS

• DNS Lookups

• Client DNS Configurations

• DHCP

• DHCP Server

• DHCP Relay

• DHCP Client

• Other DHCP Assigned Parameters

• NTP Server

• NTP Client

• Stratum

• FHRP

• HSRP

• Priority

• Preemption

• Version

Topic: Describe DNS lookup operation

Imagine a world where we would need to communicate with devices on the Internet (or our company’s intranet) using the IP addresses of systems. This would be nearly impossible since IP addresses are so difficult to memorize for the many devices. The Domain Name System (DNS) prevents this nightmare.

DNS resolves “friendly” names like www.cbtnuggets.com to the IP address that devices truly need to reach the remote system. We use DNS every day, as you might guess. The system can refer to a private RFC 1918 address space inside your organization or to the public, globally routable IPv4 address space on the Internet. You can also have your internal private DNS servers interact with public DNS servers.

The Domain Name System delegates the responsibility of assigning domain names and mapping those names to Internet resources by designating authoritative name servers for each domain. Network administrators may delegate authority over sub-domains of their allocated name space to other name servers. This approach gives us a fault-tolerant design and eliminates the need for everyone to rely on one single huge database.

Remember, when you hear DNS, you are talking about this structure of naming as well as the technical details of the protocol itself (for example, what messages are exchanged and how data is processed in the system).

The Internet maintains the domain name hierarchy and the Internet Protocol (IP) address spaces. DNS maintains the domain name hierarchy and provides translation services between it and the address spaces. A DNS name server is a server that stores the DNS records for a domain; a DNS name server responds with answers to queries against its database.

The most common types of records stored in the DNS database are as follows:

• Start of Authority (SOA)

• IP Addresses (A and AAAA)

• SMTP Mail Exchangers (MX)

• Name Servers (NS)

• Pointers for Reverse DNS Lookups (PTR)

• Domain Name Aliases (CNAME)

DNS databases are traditionally stored in structured zone files.

CramQuiz

1. Which statement about DNS is false?

• A. DNS operates thanks to one central master database.

• B. DNS resolves domain names to IP addresses.

• C. DNS uses many types of records to do its job.

• D. Multiple DNS servers are typically available for a client.

2. What device is responsible for each DNS domain?

• A. Master DNS

• B. Authoritative name server

• C. Zone file server

• D. DNS client

CramQuiz Answers

1. A is correct. The DNS system creates a distributed database so that one central master database does not need to be relied upon.

2. B is correct. Each domain has an authoritative name server that helps manage the domain.