Another type of problem that you might have is network issues.
So what are common network issues?
You may have a wrong subnet mask.
All nodes in the same network should be in the same subnet
or a wrong router.
The router must always be in the local network
or DNS is not working, in which case
you can verify the etcresolve.contents.
Now let me introduce a problem and let's
see how we can troubleshoot.
All right, let's do some troubleshooting.
Now what's the use case?
Well, ping google.com.
Oh no, doesn't work.
Now the good thing is that I do get an IP address,
but that might have been obtained from a cache
and I get destination host unreachable
and we need to analyze.
How do we analyze?
Well, use IPA, which is short for IP address show,
and look if it matches your expectations.
I can see 192.168.29.100.24.
That sounds OK.
IP route show.
And what do we see?
Oh boy, I can see a default via 192.168.28.2.
And that is not good because the 28 network is not
the same as the 29 network.
The subnet mask slash 24 means that this is the network part,
192.168.29, and the router always
must be in the same network.
And here we have a router in a different network.
That's not going to work.
And as a result, a command like ping 8888 is not working
and everything else isn't working either.
So what are we going to do about it?
Well, IP route Dell default would be an option
to delete it and IP route add default via 192.168.29.2.
Notice at first I'm doing it runtime
because I want to know if this fixes the problem.
Yeah, it fixes the problem.
Then I'm using NMTUI because apparently the problem
is somewhere in the consistent configuration using
edit and look at that.
There we have the gateway set to 28.2.
That must be 29.2.
So let's change it and click OK and do a back
and activate the connection.
First deactivate and activate it again.
And then I can quit.
And then we should be good.
So ping google.com.
And this time it is working.
Now additional troubleshooting might
involve having a look at the resolve.conf.
So etc.resolve.conf.
Well, that seems to be set correctly.
You might want to use trace path to your destination.
But trace path in many cases doesn't
give you anything because of filtering
on the in-between routers.
In the past, this was quite useful.
Nowadays, it's not so useful anymore.
Also, dig allows you to verify DNS entries.
If all is looking good, dig on your DNS name
should give you no error.
And if you do dig on something that doesn't exist,
then you get an NX domain.
NX domain means that your requested host
could not be found in DNS.
And that might mean two things.
Either in the worldwide DNS there's something wrong,
or you made a typo in your host name.
And this is about all that you can do
about network troubleshooting.