Linux Networking Concepts -Part 2
Network issues are the most common issues that have to be debugged with infrastructure and operations tasks.
Let’s take an example that, we have to debug an issue about the incoming traffic in NAT Box! How will you approach this issue?
Generally what are the steps will you be coming across?
Checking if the DNS is working correctly!
Checking if the service is up!
Checking the correct route!?
In all the steps, the first is to check if the external service DNS is resolved or not!?
It can be run through dig external_service_dns
By running telnet, it will give you if it’s not resolvable!
How to check whether the DNS is reached NAT Box?
We can do with traceroute external_service_dns
This will show that the route it is taking to reach the external service, this should go through your NAT box.
If it is not going through your NAT box it is again an issue.
Now we have to check our routes of the subnet in which our internal apps are deployed.
The external service may be rejecting the request because it is not coming from a NAT box.
To fix this issue, we have to add a route in the app’s subnet to route any traffic that has to go out should go through the NAT box.
Apart from these, there might be issues likeIP forwarding not active on the NAT box.
How would you check the connection between two machines?
telent host port works well to check the connection between two machines.
How would you count all opened files?
lsof/wc-l
Explain about Procfs?
Proc filesystems in an Unix Environment keeps track of the processes that run and other system information like Memory, CPU, IO.
The details can be found within the /proc directory and PID Processes running within the directory inside it.
Creating an Empty file?
By using touch command, we can create an Empty file.
touch file_name
Where do you find configs file?
/etc, configs file can be found in this folder.
Explain about /etc/resolv.conf file
The path generally contains the nameservers that our machine needs to query and other options like timeout and retries.
Explain about curl host:port/resource!
Making a request using terminal? this command comes in handy to make the request
Normal Size of a jumbo frames and normal size of a packet in a network
Standard Ethernet frames has 1518 bytes in size and jumbo frames are generally bigger than 1518 bytes.
