DNS Records and HTTP Web Services

Category: network-services · Difficulty: beginner · Lab ID: PTL-0022 · Document: reviewed · Simulator: tested pass

The Domain Name System (DNS) is one of the core foundation protocols of the modern Internet and enterprise intranets, translating human-friendly Fully Qualified Domain Names (FQDNs)—such as web.corp.local or www.corp.local—into machine-routable IPv4 addresses. Without DNS, users would be required to remember numeric IP addresses for every network resource, file share, and web service.

At the application layer, the Hypertext Transfer Protocol (HTTP) relies directly on DNS: when a client browser requests a website using a Uniform Resource Locator (URL), the client operating system first queries its configured DNS resolver to obtain the target server's IP address. Once the IP address is resolved, the client initiates a TCP three-way handshake on port 80 to establish an HTTP session and request web resources.

In this laboratory, you will explore the relationship between DNS name resolution and HTTP web services in Cisco Packet Tracer. You will configure an authoritative internal DNS server (DNS-Server), populate Address (A) resource records and Canonical Name (CNAME) alias records, configure client workstation resolvers across a routed enterprise boundary, and test end-to-end web delivery using nslookup, command-line tools, and web browser clients.

Learning Objectives#

• Explain the architecture, protocol operation, and hierarchical role of the Domain Name System (DNS).
• Differentiate between primary DNS resource record types, including Address (A) records and Canonical Name (CNAME) alias records.
• Configure and activate authoritative DNS services on Cisco Packet Tracer server endpoints.
• Configure and manage an HTTP web server, defining custom web portal pages.
• Configure IPv4 network settings, default gateways, and DNS server addresses on client workstations.
• Query and inspect DNS name resolution across subnets using the nslookup command-line utility.
• Verify HTTP web page delivery over resolved domain names using the client web browser.
• Troubleshoot common name resolution faults, including disabled services, record typos, and missing alias targets.

Prerequisites#

• Basic understanding of IPv4 addressing, subnet masks, and default gateways.
• Completion of PTL-0014: Default Gateway Troubleshooting or equivalent basic routing knowledge.
• Familiarity with client command-line utilities (ping, ipconfig, nslookup).
• Cisco Packet Tracer 8.2 or newer (Packet Tracer 9.0+ verified).

Topology#

The topology models an enterprise network divided into a client access subnet and a datacenter server farm connected through an inter-subnet router (R1):

[PC-1]──Fa0 ───── Fa0/1──[Switch S1]──Gi0/1 ───── Gi0/0/0──[Router R1]
(192.168.10.10)          (Client LAN)                       │ (Gateway Router)
                                                             │ Gi0/0/1 (192.168.20.1/24)
[PC-2]──Fa0 ───── Fa0/2──────────────────────────────────────┘
(192.168.10.20)                                            [Switch S2]
                                                             │ (Server Farm LAN)
                                       ┌─────────────────────┴─────────────────────┐
                                  Fa0/10                                      Fa0/11
                                       │                                           │
                                  [DNS-Server]                                [Web-Server]
                                 (192.168.20.50)                             (192.168.20.80)

Addressing Table#

DNS Resource Records#

Lab Tasks#

1. Verify physical cabling and inspect IP configuration across all endpoints and switches in the starter topology.
2. Confirm Layer 3 routing by pinging from PC-1 (192.168.10.10) to Web-Server (192.168.20.80) using its direct IP address.
3. Test initial DNS resolution by running nslookup web.corp.local on PC-1, and observe that the query fails because DNS service is unconfigured.
4. On DNS-Server, navigate to the Services tab, select DNS, and set the service to On.
5. Add an A Record named web.corp.local pointing to 192.168.20.80.
6. Add a CNAME Record named www.corp.local with Host Name web.corp.local.
7. Add an A Record named portal.corp.local pointing to 192.168.20.80.
8. On Web-Server, verify that the HTTP service is turned On and contains an index.html file.
9. Verify name resolution from PC-1 using nslookup web.corp.local and nslookup www.corp.local.
10. Verify name resolution from PC-2 using nslookup portal.corp.local.
11. From PC-1, open the Web Browser application and navigate to http://www.corp.local to verify HTTP page delivery.
12. Perform fault injection: simulate a broken DNS record by removing portal.corp.local, verify client lookup failure, and restore the record to confirm recovery.

Configuration Walkthrough#

1. Baseline Verification in Starter State#

Open the starter activity file (assets/starter.pkt). Verify that client PC-1 can reach Web-Server using its IP address across router R1:

PC-1> ping 192.168.20.80

Pinging 192.168.20.80 with 32 bytes of data:

Reply from 192.168.20.80: bytes=32 time<1ms TTL=127
Reply from 192.168.20.80: bytes=32 time<1ms TTL=127
Reply from 192.168.20.80: bytes=32 time<1ms TTL=127

Ping statistics for 192.168.20.80:
    Packets: Sent = 3, Received = 3, Lost = 0 (0% loss)

Now execute an nslookup query for web.corp.local:

PC-1> nslookup web.corp.local

Server: [192.168.20.50]
Address:  192.168.20.50
DNS request timed out.

The ping succeeds because router R1 has active routes for both 192.168.10.0/24 and 192.168.20.0/24. However, nslookup times out because the DNS service on DNS-Server is currently disabled.

2. Configure the Authoritative DNS Server#

Click on DNS-Server, navigate to the Services tab, and select DNS in the left menu:

1. Click the On radio button to enable the DNS Service.
2. In the Resource Records section:
   • Name: web.corp.local
   • Type: A Record
   • Address: 192.168.20.80
   • Click Add.
3. Create the CNAME alias:
   • Name: www.corp.local
   • Type: CNAME
   • Host Name: web.corp.local
   • Click Add.
4. Create the secondary portal A record:
   • Name: portal.corp.local
   • Type: A Record
   • Address: 192.168.20.80
   • Click Add.

Verify that all three records appear in the DNS database table.

3. Verify HTTP Web Service on Web-Server#

Click on Web-Server, navigate to the Services tab, and select HTTP:

1. Ensure the HTTP service radio button is set to On.
2. Locate index.html in the file list. The default Cisco Packet Tracer page or custom portal content should be present:

<html>
<head><title>Corporate Intranet Portal</title></head>
<body>
<h1>Welcome to Corporate Intranet</h1>
<p>DNS and HTTP services operational.</p>
</body>
</html>

4. Verify Client DNS Configuration#

Click on PC-1, open Desktop -> IP Configuration, and verify that the DNS Server field is set to 192.168.20.50. Check PC-2 to ensure its DNS Server is also set to 192.168.20.50.

Verification#

1. Test A Record Resolution with nslookup#

On PC-1, open the Command Prompt and test primary A record resolution:

PC-1> nslookup web.corp.local

Server: [192.168.20.50]
Address:  192.168.20.50

Non-authoritative answer:
Name:   web.corp.local
Address:   192.168.20.80

The internal DNS server (192.168.20.50) successfully responded with the IPv4 address 192.168.20.80.

2. Test CNAME Alias Resolution#

From PC-1, resolve the alias hostname www.corp.local:

PC-1> nslookup www.corp.local

Server: [192.168.20.50]
Address:  192.168.20.50

Non-authoritative answer:
Name:   web.corp.local
Address:   192.168.20.80

Aliases:   web.corp.local

The DNS server returned the alias mapping: www.corp.local points to canonical name web.corp.local, which resolves to IP 192.168.20.80.

3. Test Secondary A Record Resolution#

On PC-2, query the secondary portal record:

PC-2> nslookup portal.corp.local

Server: [192.168.20.50]
Address:  192.168.20.50

Non-authoritative answer:
Name:   portal.corp.local
Address:   192.168.20.80

Both workstations independently resolve enterprise hostnames through the central DNS server.

4. Access Web Service via FQDN in Web Browser#

On PC-1, close the Command Prompt, open the Web Browser application on the Desktop, and enter: http://www.corp.local

Click Go. The browser resolves www.corp.local to 192.168.20.80 via DNS and displays the intranet web page:

Welcome to Corporate Intranet
DNS and HTTP services operational.

Troubleshooting#

Key Takeaways#

• Separation of Concerns: DNS resolves human-readable names to network addresses; HTTP delivers application web content over established transport sessions.
• Record Types:
  • A Record (Address): Maps a hostname directly to an IPv4 address (web.corp.local -> 192.168.20.80).
  • CNAME Record (Canonical Name): Creates an alias pointing to an existing A record (www.corp.local -> web.corp.local), enabling multiple service names to share a single host record.
• Client Resolution Process: When an application requests an FQDN, the client OS queries the configured DNS server using UDP port 53. The returned IP is used for subsequent Layer 3/4 communication.
• Enterprise Centralization: A central DNS server serves multiple client subnets across an enterprise router, provided routing and default gateways are configured correctly.

References#

• IETF RFC 1034: Domain Names — Concepts and Facilities
• IETF RFC 1035: Domain Names — Implementation and Specification
• IETF RFC 7230: Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
• Cisco CCNA 200-301 Official Cert Guide: IP Services and Name Resolution

Files and Validation Status#