Domain Name Service is what resolve hostnames to IP addresses. When you have DNS server running on your network, you don’t have to type the IP address of the host you want to connect to or ping as long as a hostname is set. You just type the hostname, Internet name or Fully qualified domain name(fqdn) and DNS server work out the rest for you.
DNS Server listens on UDP port 53.
We’ll use topology shown below to setup DNS server. R1 will use R2 as DNS server to make DNS resolutions.
First, let’s begin with R1. We’ll setup hostname and IP related information.
R1 ip Configurations:
enable configure terminal hostname R1 interface e0/0 ip address 10.10.10.1 255.255.255.0 no shut do wr end
R2 IP and Hostname Configurations
enable config t hostaname R2 int e0/0 ip address 10.10.10.2 255.255.255.0 no shut do wr end
Setting up R2 as DNS Server
config t ip dns server ip host loopback.R2.com 188.8.131.52
We mapped loopback.R2.com to ip address 184.108.40.206. Currently, we don’t have 220.127.116.11, we could create loopback interface on R2 and assign ip 18.104.22.168
interface loopback 1 ip address 22.214.171.124 255.255.255.255 end
Let’s verify that loopback interface we just created is working.This will show us that the hostname correctly setup locally on R2.
Now it’s time to setup R1 to resolve hostnames using R2.On R1 type;
config terminal ip domain lookup ip name-server 10.10.10.2
Set R1 to use R2 as the default gateway to get to the loopback interface on R2. So that after R1 resolve loopback.R2.com, it can reach 126.96.36.199 through its default route (R2).
on R1 type:
config t ip route 0.0.0.0 0.0.0.0 10.10.10.2 end
This tells our router that to get to any network not in its routing table, it’s next hop is 10.10.10.2 which is our router R2.
We can turn on DNS udp port debug command so that we can see what’s going on on R1.
debug ip udp
Now on R1, do a ping to loopback.R2.com and you should get a success message.
ping loopback.R2.com repeat 3
If you captured the traffic, you’ll see DNS query and Answer as shown in Wireshark capture screenshot below.