A distributed denial of service (DDoS) attack is a concerted malicious attack that generates a huge amount of traffic in one go to bring down a service provider. If a high-level DNS server goes down in this way, it can disrupt services such as the Amazon cloud service or Azure services worldwide. By typing the command "ping 8.8.8.8" into your command line, you can ping Google's DNS server. A successful ping usually means that layers 1, 2, and 3 are all working as expected.
Traceroute is a command you can enter that sends "echo" requests that trace the routes and IP addresses a packet passes through during a request. Run a traceroute by typing “tracert 8.8.8.8”. A traceroute pings each server and follows the route from your device to Google's DNS server. On a Linux-based machine, you would type "traceroute 8.8.8.8" instead.
If you run a ping and traceroute command, you have diagnosed that up to layer 3, your Internet connection is working.
During DNS resolution, queries are made to DNS servers to obtain IP addresses. If the DNS server does not know the IP address of the domain name in question, it forwards the query upstream. “nslookup google.com” will check if the external DNS lookup is working correctly. If you want to override the default and set your own DNS server, you can type "nslookup", which takes you to a command prompt where you can add additional parameters to the setting, including specifying the DNS server you want to use , like 8.8. 8.8.
0:00 – Introduction to troubleshooting external network issues
0:45 – Why people will inevitably stand over your shoulder to tell you the internet is down
2:10 – A diagram of the differences between internal networks and external Internet
4:25 – How do service provider connections work in the real world?
5:50 p.m. – What are DDoS attacks and how they affect connectivity
7:40 a.m. – How a misconfigured BGP server caused the entire East Coast of the United States to lose Internet
8:50 a.m. – Using the command line to ping Google's DNS server to diagnose whether resources on the public Internet are available
10:15 – Using traceroute to trace the router and the IP address it passes through during a request
2:25 p.m. – How DNS IP address requests tend to get resolved and how they can go wrong
4:00 p.m. – How to test external DNS resolution and reconfigure your nslookup command with unique parameters
Watch this entire course: https://training.cbt.gg/ova
Not a CBT Nuggets subscriber? Start your free week: https://www.cbtnuggets.com/signup
—————–
Connect with CBT Nuggets to get the latest IT training:
• Twitter – https://twitter.com/CBTNuggets
• Facebook – http://facebook.com/CBTNuggets
• Instagram – http://instagram.com/CBTNuggets
• LinkedIn – https://www.linkedin.com/company/cbt-nuggets
#network #dnsserver #internetisdown #ittraining #cbtnuggets
Please take the opportunity to connect and share this video with your friends and family if you find it useful.
No Comments