Cisco Domain Name Lookup Guide

Cisco domain name lookup is an essential feature that allows users to connect to websites and apps on the internet by typing in the website’s domain name instead of its IP address. In this blog post, we will discuss the basics of Cisco domain name lookup and how to configure it on Cisco routers.

What is Cisco Domain Name Lookup?

The domain name system (DNS) is sometimes referred to as the “phone book” of the Internet. It is a standard that defines a domain naming procedure used in TCP/IP. A domain is a hierarchical separation of the network into groups and subgroups with domain names. DNS has three basic functions: Name space, Name registration, and Name resolution.

Cisco domain name lookup is a feature that allows users to connect to websites and apps on the internet by typing in the website’s domain name instead of its IP address. When a user types in a domain name, the Cisco router queries the DNS server to resolve the domain name to its corresponding IP address.

How to Configure Cisco Domain Name Lookup?

To configure Cisco domain name lookup, we need to follow some basic configuration steps. These steps are:

  1. Enable DNS Server: To enable DNS Server on the router, we will use the “ip dns server” command. With this command, our router becomes a DNS Server.
RouterA # configure terminal
RouterA (config)# ip dns server
  1. Enable Domain Lookup: To enable domain lookup, we will use the “ip domain lookup” command. With this command, the router can query to the configured public DNS Servers if the record does not exist in it.
RouterA (config)# ip domain lookup
  1. Public Name Server Configuration: In this step, we will configure Public Name Servers. If the requested record does not exist in the router’s cache, the router queries the configured public DNS servers.
RouterA (config)# ip name-server 8.8.8.8
RouterA (config)# ip name-server 8.8.4.4
  1. Host / IP Address Mappings: We will define hostname-ip matchings manually. But what if there is a query different than them? At this time, the router will query to an upper DNS Server that we will configure in the next step.
RouterA (config)# ip host www.google.com 172.217.168.196
  1. Router Interface IP Configuration: We need to configure the IP address of the router interface.
RouterA (config)# interface GigabitEthernet0/0/0
RouterA (config-if)# ip address 192.168.1.1 255.255.255.0
  1. Hosts IP Configuration: We need to configure the IP address of the hosts.
PC1(config)# ip address 192.168.1.2 255.255.255.0
PC2(config)# ip address 192.168.1.3 255.255.255.0
  1. Configuration Verification: We can verify the configuration using the “show ip dns” command.
RouterA# show ip dns

how to troubleshoot DNS issues on Cisco routers

Troubleshooting DNS issues on Cisco routers can involve several steps depending on the nature of the problem. Here’s a general approach you can follow:

1. Gather Information:

  • Symptom Identification: Clearly define the issue you’re facing. Is it complete lack of domain resolution, slow resolution, or specific domain failures?
  • Device Details: Note the model and operating system version of your Cisco router.
  • Configuration Review: Check your DNS server configuration using show ip dns and verify if they are reachable with ping.

2. Basic Checks:

  • Connectivity: Ensure basic network connectivity with ping commands to internal and external IPs.
  • DNS Server Reachability: Ping the configured DNS servers to confirm they are online.
  • Firewall Rules: Verify if any firewall rules are blocking DNS traffic (port 53).

3. Advanced Troubleshooting:

  • nslookup Tool: Use nslookup to manually query DNS servers and identify issues at specific stages.
  • Debug Commands: Enable relevant debug commands based on your issue (e.g., debug ip name-resolver, debug ip dns) but be cautious as debugging can generate significant output.
  • Packet Capture: Capture network traffic (use Wireshark or similar tools) to analyze DNS requests and responses for errors or delays.
  • Cisco Documentation: Refer to the official documentation for your router model and OS for specific troubleshooting steps and known issues.

4. Additional Resources:

  • Cisco Learning Network: Search for discussions and solutions related to your specific issue on the Cisco Learning Network forums.
  • Cisco TAC (Technical Assistance Center): For more complex issues, consider contacting Cisco TAC for paid support.

Remember:

  • Always back up your router configuration before making changes.
  • Enable debugging commands cautiously and disable them afterward to avoid overloading your device.
  • If you’re unsure about any steps, consult a network administrator or seek professional help.

By following these steps and utilizing the available resources, you should be able to effectively troubleshoot DNS issues on your Cisco router. If you can provide more specific details about your situation, I might be able to offer more tailored guidance.

Conclusion

In conclusion, Cisco domain name lookup is an essential feature that allows users to connect to websites and apps on the internet by typing in the website’s domain name instead of its IP address. In this blog post, we discussed the basics of Cisco domain name lookup and how to configure it on Cisco routers. By following the steps mentioned above, users can easily configure Cisco domain name lookup on their routers.

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