Cisco IOS Configure Router as DNS Server
Network Topology
To create this topology, I used GNS3 instead of Cisco Packet Tracer because Packet Tracer routers do not simulate the "ip dns server" command. In the above network Router0 is being configured as a DNS server. Through the configuration of Router0 I wanted to not only demonstrate the ability for the router to resolve local hosts on the network, but I also wanted to show how DNS resolution that Router0 was unable to do could be forwarded to a real DNS server (1.1.1.1) on the Internet. In this way Router0 has been configured to forward unknown requests to the Cloudflare and APNIC's DNS server at 1.1.1.1. I also decided to use a real Windows 2016 Server appliance in the topology. I could have just as easily used another VPCS QEMU device, but it gave me an opportunity to revisit GNS3 Windows appliances. Also, it is not the best practice to use a networking router as the DNS server, but it can be done as this shows.
Router0 Configuration Commands
Router0>enable
Router0#configure terminal
Router0(config)# interface gigabitEthernet 0/0
Router0(config-if)#ip address 192.168.10.1 255.255.255.0
Router0(config-if)#no shutdown
Router0(config-if)#interface gigabitEthernet 0/1
Router0(config-if)#ip address 172.16.1.1 255.255.255.248
Router0(config-if)#no shutdown
Router0(config-if)#exit
Router0(config)#ip dns server
Router0(config)#ip domain-name local
Router0(config)#ip name-server 1.1.1.1
Router0(config)# ip host fileserver.local 192.168.10.2
Router0(config)# ip host pc1.local 192.168.10.3
Router0(config)# ip host pc2.local 192.168.10.4
Router0(config)# ip host router0.local 192.168.10.1
Router0(config)# ip host router1.local 172.16.1.2
Router0(config)# ip host router2.local 172.16.2.1
Router0(config)# ip default-network 192.168.2.0
Router0(config)# router ospf 1
Router0(config-router)# network 172.16.1.0 0.0.0.7 area 0
Router0(config-router)# network 192.168.10.0 0.0.0.255 area 0
Router1 Configuration Commands
Router1>enable
Router1#configure terminal
Router1(config)# interface gigabitEthernet 0/0
Router1(config-if)#ip address 172.16.1.2 255.255.255.248
Router1(config-if)#no shutdown
Router1(config-if)#interface gigabitEthernet 0/1
Router1(config-if)#ip address 172.16.2.2 255.255.255.248
Router1(config-if)#no shutdown
Router1(config-if)#exit
Router1(config)#ip name-server 172.16.1.1
Router1(config)# ip default-network 192.168.2.0
Router1(config)# router ospf 1
Router1(config-router)# network 172.16.1.0 0.0.0.7 area 0
Router1(config-router)# network 172.16.2.0 0.0.0.7 area 0
Router2 Configuration Commands
Router2>enable
Router2#configure terminal
Router2(config)# interface gigabitEthernet 0/0
Router2(config-if)#ip address dhcp
Router2(config-if)#no shutdown
Router2(config-if)#ip nat outside
Router2(config-if)#interface gigabitEthernet 0/1
Router2(config-if)#ip address 172.16.2.1 255.255.255.248
Router2(config-if)#no shutdown
Router2(config-if)#ip nat inside
Router2(config-if)#exit
Router2(config)#ip nat inside source list 1 interface gigabitEthernet0/0 overload
Router2(config)#access-list 1 permit any
Router2(config)# router ospf 1
Router2(config-router)# network 192.168.2.0 0.0.0.255 area 0
Router2(config-router)# network 172.16.2.0 0.0.0.7 area 0
The configuration of nat on Router2 is so that the network can communicate to the connected network and then to the Internet through the GNS3 cloud object. I did this to demonstrate the DNS forwarder on Router0 to 1.1.1.1 Also, the IP address on gigabitEthernet 0/0 is set for DHCP as it is getting an address from my network DHCP server. You could also make this a static address if desired. If you do set a static IP address, remember to configure a gateway of last resort. The DHCP setting configures that for the interface automatically.
Check DNS (a few ping examples)
PC1>ping fileserver.local
PC1>ping router2.local
PC1>ping www.google.com
Check the configured DNS Hosts on Router0
Router0#show hosts
