Dedicated DNS & Name Resolution Lab (Packet Tracer)¶

Theory prerequisites

Read TCP vs UDP, DNS & Ports, and HTTP/HTTPS & TLS. Return to the Lab-Aligned Learning Path after verification.

This lab introduces Domain Name System (DNS) concepts from the ground up. You will learn how human-friendly hostnames (such as www.company.local and ftp.company.local) are resolved into IP addresses across different subnets.

You will configure:

A Records (Address Records): Mapping domain names directly to IPv4 addresses.
CNAME Records (Canonical Name / Alias): Aliasing secondary service names to primary domain names.
Integrated DHCP + DNS: Automatically distributing DNS server settings to client PCs.
Simulation Mode Packet Tracing: Watching a DNS UDP query (Port 53) trigger before an HTTP TCP handshake (Port 80).

Topology¶

Addressing Plan¶

Device	Interface	IP Address	Subnet Mask	Default Gateway	DNS Server	Role
Router0	`Gig0/0`	`192.168.1.1`	`255.255.255.0`	—	—	LAN 1 Gateway & DHCP Server
Router0	`Gig0/1`	`198.51.100.1`	`255.255.255.0`	—	—	LAN 2 Gateway (Server Farm)
DNS-Server0	`Fa0`	`198.51.100.5`	`255.255.255.0`	`198.51.100.1`	`127.0.0.1`	Dedicated DNS Server (Port 53)
Web-Server0	`Fa0`	`198.51.100.10`	`255.255.255.0`	`198.51.100.1`	`198.51.100.5`	HTTP & FTP Server
PC0	`Fa0`	via DHCP	via DHCP	`192.168.1.1`	`198.51.100.5`	Client PC (`192.168.1.2`)
PC1	`Fa0`	via DHCP	via DHCP	`192.168.1.1`	`198.51.100.5`	Client PC (`192.168.1.3`)

1. Place and Cable Devices¶

Devices Required¶

2x Generic PC (PC0, PC1)
2x Switch (2960-24TT: Switch0, Switch1)
1x Router (1941: Router0)
2x Server (DNS-Server0, Web-Server0)

Cabling Connections (Copper Straight-Through)¶

PC0 (FastEthernet0) <—> Switch0 (FastEthernet0/1)
PC1 (FastEthernet0) <—> Switch0 (FastEthernet0/2)
Switch0 (FastEthernet0/3) <—> Router0 (GigabitEthernet0/0)
Router0 (GigabitEthernet0/1) <—> Switch1 (FastEthernet0/1)
Switch1 (FastEthernet0/2) <—> DNS-Server0 (FastEthernet0)
Switch1 (FastEthernet0/3) <—> Web-Server0 (FastEthernet0)

2. Router0 Configuration¶

Open Router0 CLI and configure the interfaces and DHCP pool (which includes the DNS server IP address option):

enable
configure terminal
hostname Router0

! 1. Configure LAN 1 (Clients)
interface GigabitEthernet0/0
 description Client LAN
 ip address 192.168.1.1 255.255.255.0
 no shutdown
exit

! 2. Configure LAN 2 (Servers)
interface GigabitEthernet0/1
 description Server Farm
 ip address 198.51.100.1 255.255.255.0
 no shutdown
exit

! 3. Configure DHCP Pool (Points clients to DNS-Server0)
ip dhcp excluded-address 192.168.1.1
ip dhcp pool CLIENT_POOL
 network 192.168.1.0 255.255.255.0
 default-router 192.168.1.1
 dns-server 198.51.100.5
 domain-name company.local
exit

end
write memory

3. Server Configuration¶

Step A: Configure DNS-Server0¶

Open DNS-Server0 > Desktop > IP Configuration:
IP Address: 198.51.100.5
Subnet Mask: 255.255.255.0
Default Gateway: 198.51.100.1
DNS Server: 127.0.0.1 (or 198.51.100.5)
Go to Services > DNS:
DNS Service: Toggle On
Add 'A Record' (Primary Domain):
- Name: www.company.local
- Type: A Record
- Address: 198.51.100.10
- Click Add
Add 'A Record' (Apex Domain):
- Name: company.local
- Type: A Record
- Address: 198.51.100.10
- Click Add
Add 'CNAME Record' (Alias for FTP):
- Name: ftp.company.local
- Type: CNAME
- Host Name: www.company.local
- Click Add

Step B: Configure Web-Server0¶

Open Web-Server0 > Desktop > IP Configuration:
IP Address: 198.51.100.10
Subnet Mask: 255.255.255.0
Default Gateway: 198.51.100.1
DNS Server: 198.51.100.5
Go to Services > HTTP:
Toggle On for HTTP and HTTPS
(Optional) Click edit next to index.html and change the text to <h1>Welcome to Company Portal</h1>
Go to Config > Services > FTP:
Toggle On, add user cisco / password cisco with all permissions checked.

4. Client PC Configuration¶

Open PC0 > Desktop > IP Configuration:
Select DHCP.
Confirm PC0 receives an IP (192.168.1.2), Gateway (192.168.1.1), and DNS Server (198.51.100.5).
Repeat for PC1.

5. Verification and Testing¶

A. NSLOOKUP Name Resolution Test¶

Open PC0 > Desktop > Command Prompt and query the DNS server directly:

nslookup www.company.local

Expected Output:

Server:  198.51.100.5
Address: 198.51.100.5

Name:    www.company.local
Address: 198.51.100.10

Test the CNAME alias:

nslookup ftp.company.local

Expected Output shows ftp.company.local aliases to www.company.local which resolves to 198.51.100.10.

B. Web Browsing via Domain Name¶

Open PC0 > Desktop > Web Browser and navigate to:

http://www.company.local

(You will reach the Web Server page without ever typing an IP address).

C. FTP Access via CNAME¶

Open PC0 > Desktop > Command Prompt:

ftp ftp.company.local

Enter username cisco / password cisco to verify service reachability via domain alias.

6. How DNS Works Under the Hood (Simulation Mode)¶

Switch Packet Tracer to Simulation Mode (Shift + S) and filter by DNS, ICMP, and HTTP:

On PC0 Web Browser, enter http://www.company.local and press Enter.
Step through the packets:
Step 1 (DNS Query): PC0 encapsulates a DNS query into a UDP packet with destination port 53 addressed to 198.51.100.5.
Step 2 (Routing): Router0 forwards the UDP packet across subnets from Gig0/0 to Gig0/1.
Step 3 (DNS Response): DNS-Server0 looks up its database and sends back a DNS Answer: www.company.local = 198.51.100.10.
Step 4 (HTTP Connection): Now that PC0 knows the IP address, it initiates a TCP 3-way handshake (SYN, SYN-ACK, ACK) to 198.51.100.10:80 followed by an HTTP GET request.

7. DNS Key Concept Reference¶

Concept / Record	Purpose	Example from Lab
A Record	Maps a domain name (FQDN) to an IPv4 address.	`www.company.local` → `198.51.100.10`
CNAME Record	Creates an alias pointing one name to another canonical name.	`ftp.company.local` → `www.company.local`
Port 53 (UDP vs TCP)	Standard DNS queries use UDP 53 for low latency; large transfers/zone transfers use TCP 53.	PC queries to `198.51.100.5:53`
Hierarchical Resolution	In production, if a local DNS server cannot resolve an address, it forwards queries up to Root servers, TLD servers, and Authoritative servers.	In this lab, DNS-Server0 is authoritative for `.company.local`.