» Linux » Examen sur Linux » Examen 202 : Networking Administration » Section 3 » Question 5/20
5.Several users complain that when checking their email or telnetting to your server they have to wait up to 60 seconds before getting their email or being presented with a login screen. However, immediately successive attempts at the same operation succeed normally – only to suffer again from the same problem after some time. What is causing this behavior?

The DNS server used by the clients is not properly resolving the server name to an ip address.
The routing table on the server contains multiple routes to the client’s machines.
The server is timing-out while trying to resolve the client’s IP addresses to names.
A router along the way is dropping packets in transit.
Another machine on the server’s network is using the same IP address.

Explanation: When you connect to a Linux server to collect email or via Telnet, the server looks at your IP address and then tries to resolve it to a hostname to check whether the hostname is allowed to connect. This is known as a reverse DNS lookup. The cause of the problem is that the server is timing out while performing the IP address to hostname resolution.

Incorrect Answers
A: If the DNS server used by the clients is not properly resolving the server name to an IP address, the clients would never be able to connect using the server hostname.
B: The server would use the route with the lowest cost if multiple routes existed.
D: This is possible, but it is not the most likely cause of the problem. You would get an error message is the packets were being dropped.
E: An IP conflict is unlikely to be the cause of the problem.
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