What is a DNS flood attack?

A DNS flood attack is a type of Distributed Denial of Service (DDoS) attack. It targets the DNS server, which is crucial for translating domain names (like www.example.com) into IP addresses that computers use to communicate. The attack floods the DNS server with an overwhelming number of requests, causing legitimate traffic to be delayed or completely blocked, effectively taking the service offline.

How does a DNS flood attack work?

Imagine a small post office suddenly receiving millions of letters, most with incorrect return addresses. A DNS flood attack operates similarly. Attackers leverage a network of compromised devices, known as a botnet, to send a deluge of DNS requests to a target server. These requests are often disguised with fake IP addresses, adding confusion and preventing easy filtering. The server, inundated by this tsunami of requests, struggles to respond, leading to legitimate requests being ignored or delayed – effectively disrupting normal web services. 

Let’s break down the process into steps:

1. Volume of traffic: The attacker sends a massive amount of DNS requests to the target server, often using a network of compromised computers (botnets).
2. Spoofing IP addresses: These requests often have fake return addresses, making it hard for the server to distinguish between legitimate and illegitimate traffic.
3. Server overload: The DNS server becomes overwhelmed, trying to process each request, leading to slowed down services or a total shutdown.
4. Secondary effects: The attack can also impact other services that rely on the DNS server, creating a ripple effect of disruption.

Why is it dangerous?

The danger of DNS flood attack cannot be overstated. They are more than just an inconvenience; they pose a significant threat to online operations. Firstly, they can cause major disruptions to essential services, crippling websites and online platforms. This disruption can have a cascading effect, impacting not only the targeted site but also any service that relies on it. The financial implications are equally severe, especially for businesses that depend on online transactions or services. Beyond the immediate financial losses, these attacks can inflict long-term damage to a company’s reputation, shaking customer confidence and trust. Moreover, while the focus is on mitigating the attack, other security vulnerabilities might be overlooked, leaving the door open for further exploits.

How to recognize a DNS flood attack?

Identifying a DNS flood attack primarily involves monitoring for an abnormal surge in DNS traffic. This is where tools like ClouDNS Free DNS tool come into play. This innovative tool enables users to inspect DNS records for specific hosts and analyze the speed and volume of DNS queries. Users can conduct a thorough audit of their DNS traffic, a crucial step in early detection. The tool’s user-friendly interface and comprehensive functionality, including compatibility with major DNS resolvers like Cloudflare, make it an invaluable resource in a cybersecurity toolkit.

DNS flood attack mitigation

To defend against DNS flood attacks, consider the following strategies:

DNSSEC (Domain Name System Security Extensions):

DNSSEC adds an extra layer of security by verifying the authenticity of DNS responses. This helps ensure that the data hasn’t been altered, making it harder for attackers to exploit the DNS system.

DDoS Protection Service:

DDoS Protection services specialize in distinguishing and mitigating abnormal traffic patterns characteristic of DDoS attacks. They can redirect malicious traffic, keeping your DNS server operational.

DNS Monitoring:

Regularly monitoring DNS traffic for unusual patterns helps in early detection of potential attacks, allowing for swift action before significant disruption occurs.

Enabling DNS Caching:

DNS caching reduces the load on servers by storing responses locally. During an attack, cached data can still be served, maintaining service availability for some users.

Secondary DNS:

A Secondary DNS provides redundancy. If your primary server is overwhelmed, the secondary server can maintain service availability, minimizing downtime.

DoT (DNS over TLS) and DoH (DNS over HTTPS):

Implementing DoT and DoH encrypts DNS queries, enhancing security. They help differentiate legitimate traffic from malicious queries, as most attack traffic doesn’t use these secure channels.

Conclusion

In summary, effectively mitigating DNS flood attacks involves a blend of strategic defenses and proactive monitoring. By adopting a range of protective measures and staying vigilant, organizations can safeguard their online presence against these disruptive threats. Remember, a robust defense is essential in maintaining the integrity and reliability of your digital services in today’s interconnected world.

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What is DNS_PROBE_FINISHED_NXDOMAIN?

It is a DNS-related error that shows that the domain that you are trying to reach does not exist (NXDOMAIN means non-existing domain). The DNS can’t find the corresponding IP address to the domain you just entered.
Most of the times this is a DNS configuration problem, and the problem is in your device, not in the domain itself.

Ok, we said Chrome, but does this happen when you are using other browsers?

We mention Google Chrome, where you get “This site can’t be reached,” but you can get a similar message in any other browser. Mozilla’s Firefox will show you “Hmm. We’re having trouble finding that site”, Microsoft Edge “Hmmm… can’t reach this page”, and almost identical messages on the rest of the browsers.

Ok, so what to do when we see the DNS_PROBE_FINISHED_NXDOMAIN?

There are several ways that you can fix your problem. Let’s explore the possibilities:

1.    Flush the DNS cache

If it is bad-configured DNS, the easiest is to start from zero. Flush the current DNS cache and renew the IP address.

For Windows users, follow these steps:
Open the Command Prompt as an administrator. Click the start menu icon and write “Command Prompt,” then run as administrator. Then type “ipconfig /release” and press Enter on your keyboard. Now you can see your current IP address. After that, write “ipconfig /flushdns” and press Enter. You flushed the cache, “Successfully flushed the DNS Resolver Cache.” Next thing to type in “ipconfig /renew”. And now your IP address has been renewed.

For Mac OS users:
Go to “System Preferences…”, then “Network” and later “Advanced.” When you are there, go to TCP/IP and click the “Renew DHCP.”
You can also delete the DNS cache. First, open the “Utilities” and then the “Terminal.” The command you need to write is “dscacheutil –flushcache” and press Enter. It is ready. There is no confirmation message here.

For Linux (Linux Mint, Ubuntu):
If you are using Linux Mint or Ubuntu, by default, the DNS cache is disabled. You can check if it is enabled with the following command “ps ax | grep dnsmasq”. In the message that you’ll get check if “cache-size=0”, then it is disabled. If it is enabled, write the following command “udo /etc/init.d/dns-clean restart”. Then type “sudo /etc/init.d/networking force-reload”. Done!

2.    Reinitiate the DNS Client Server.

For Windows users, we will use the “Run” to open “services.msc.” Now you will see all the services that run on your computer. Go to DNS Client, stop it and start it again.

3.    Change the DNS servers

Your internet provider automatically set your IP address, using their DNS servers. But you have the chance to change to another DNS server like Google’s public DNS.

Windows:
Go first to “Control Panel,” then “Network and Internet” and later “Network and Sharing Center.” There click the “Change adapter settings” and select the network that you are using. Go to properties, search for the “Internet Protocol Version 4” and click on the properties. Set the following DNS servers 8.8.8.8 and 8.8.4.4

Mac OS:
“System Preferences,” Network,” and then “Advanced.” Click on DNS and add the same 8.8.8.8 and 8.8.4.4.

Linux (Linux Mint, Ubuntu):
Open “System Settings,” “Network.” Then select the network that you are using and choose “Settings.” Go to the “IPv4 Settings,” and there you will see “Additional DNS servers.” add “8.8.8.8, 8.8.4.4”.

4.    Chrome Flags Reset.

Maybe the problem comes from your Chrome browser. Go to your Chrome browser and type “chrome://settings/clearBrowserData” in the address bar. Delete the “Cached images and files,” “Cookie and other site and plugin data” and “Browsing history” from “the beginning of time.”
After that type “chrome://flags/” and a menu will open. Click on the “Reset all to default.” Now restart the browser, and you are ready.

Conclusion

Next time when you see the DNS_PROBE_FINISHED_NXDOMAIN don’t panic. There are easy solutions to this problem. Just try one of those, and you will be ready is a few minutes.
If the site that shows the error is yours, and after trying nothing is happening, go and check if the domain is correctly redirected. If no, do fix it.

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