IP address assigned, but not reachable.
OK, so I'm sure some of you probably have experienced the issue where you do see the IP address, but
you cannot connect to that machine through S.H. or from another machine, of course, using a Secich.
So that's where we are going to focus in this lecture is about troubleshooting issues that focuses on
how and what could be the reason the machine has an IP address, but we still cannot connect or still
cannot go outside of that machine to other machines.
So the troubleshooting steps that we could go, where is the first one?
As well as check if you are on the correct network by running if config, what does it mean if you have
multiple interfaces?
So let's say if your machine has three interfaces instead of one, then you need to make sure you are
picking the right interface where you have assigned the IP address.
Because the network team now I'm talking about like virtualization team or the network team.
What they do is they if there are like cables connected in the back of a computer, then they will give
an IP address to one cable and not the other two.
So make sure the cable that is connected to the correct interface is the interface is actually being
configured for that IP address.
So we'll take a look at that in a little bit when we log into a Linux machine.
Also check to see if you got the right subnet mask and gateway.
You also you always get the subnet information and gateway information from your network engineer.
So make sure when you are talking to your network engineer, make sure they have given you the correct
subnet and correct gateway.
That might be a typo.
There might be a fat finger when they when they sent you an email instead of like one, two, once they
one one gateway a product giving it two.
And then you are just trying and figuring out so hard, but it's just not working.
Then paying the gateway if you are in the right gateway, then simply paying that gateway just to make
sure if you could reach that gateway, if you cannot reach the gateway, then of course there's something
wrong with the gateway or something wrong with the routing, which will take a look in a bit, check
if the gateway is assigned.
So if your configuration is correct, then the gateway will be a side itself.
But if it is incorrect, then most likely you will have a problem where the gateway will not show up.
So Gateway is like a gate would actually transport all your traffic from your machine to another machine.
So if the gateway is not set and the routing table, then you're going to have a problem.
Check with the network.
If the correct VLAN is a sign on the switch side, what does it mean?
It means that every network IP addresses are different.
Right?
So the IP address that that is given to you is actually assigned to the correct IP range, which is
referred to as VLAD on the switching side, if that is assigned to the correct Veillette, if you have
given an IP address, for example, one nine two one sixty eight one Dodwell and that in the back on
the switch side, it is configured for IP address 10 once every two to 16 that one.
Then no matter how many times you try, it will not work.
Your computer will be OK, you're sitting on, your computer will be OK, but the network switch side
is not OK.
So make sure when you talk to your networking folks, tell them that you are using this IP address.
Please make sure it is actually associated to the correct VLAN on the switch side.
Run tools like Ethe Tool or me tool to check the next status.
So of course if you are not at the data center, you cannot really physically verify if the cable is
connected right.
You cannot see the blinking light on the port.
So there are tools that could tell you if the link status is up or down and those tools are either tool
and I tool will check in a little, but also run the command f up space, the interface command to bring
up the next port.
Or you could just do F down and then F up just to reset the interface.
Maybe it was not set up correctly and you probably have to restart, restart network system of course,
which will do everything for you if you.
Things are not working.
Something is wrong if you're doing a system to restart a network and there is something wrong with the
network setting, it will tell you where exactly the problem is.
Check on the status of NEKE by running if config or IP address command.
We know that we ran that command many times, but on the network itself, you probably see the IP address.
You probably see it is assigned a Nika's up, but the actual the interface a NEC is probably not showing
up as yuppy meaning up.
So we will check that in a little, but also check to see if the IP is assigned to some other device.
OK, yeah, that happens to me too.
In the past, if you are trying to assign an IP, especially static IP to your machine and everything
looks good but still having a problem, then there could be a, uh, a possibility that the IP that
is given to you has already been assigned to another machine.
People make mistakes.
That's why maybe they engineered the network engineer has given you that IP, which is a duplicate IP
and is going to cause IP conflict.
So what will happen is you will try to bring your IP address up and it will come up, but it won't work
because it's already up by another computer.
Your IP address will only work when you and the other computer shuts down.
So again, make sure there's no IP conflict and sometimes there are firewalls rules in place.
Add the operating system level or at the network switch level, which will prevent you to Pangu or Sensage
from one machine to another.
So make sure your firewall is turned off at the OS level as well as the firewall configuration is done
right at the networking level.
So again, bring it up with the networking team.
Ask them if there are any issues with the firewall that has been sitting in the middle of one computer
that you're working to, another computer where you're trying to reach to zero a few troubleshooting
steps.
Let's go into our next machine and we will actually
go through all these items.
OK, this is my last machine, I have it up and running and I am logged in as root.
So now let's see first check if you are on the correct network interface.
So if I do if config or if I do IP space A or address, you'll see all the interfaces that you have
available right now.
You see, you have ENPI zero S3, L.O., which is the loop back.
This is something you don't have to worry about.
You could ignore it.
And the same way you don't have to worry about the virtual bridge adapter.
If you had NPC S3 here and you had another one zero and ENPI zero, as for S5 three of them, then you
are trying to probably assign this IP one to 161, 36, 37, seven, whatever the IP is given to you,
you probably assigning to S3.
Well in fact it should go to ENPI zero zero S4.
If that's the case, make sure you are assigning it to the correct one.
How do you know you are signing it to the correct one?
Well, the tools that you could use to check the status if the link status is up or not is by running
the e t h tool or am I too.
So if I have two interfaces, I could do it.
Tool E and p0 as three when I hit enter, you will see right here tells me the speed of this, uh interface
and somewhere here it will tell you something about like, um, yes.
All the way at the bottom.
You see it says Hlinka detected.
It says yes.
It means the cable in the back is connected.
Of course we are using virtualization, um, uh, Lennix machine, but it will still read it as if the
cable is connected.
So you see right here says Link to dictate.
Yes, perfect.
If you had any P0 as four or five and you had link detected coming up as no, then you know, right
away, OK, this IP address is not set up for that interface.
So you will assign to the correct one.
Now the question is, what if you have three interfaces, then all of them show up as link detected?
Yes.
Then basically you have to go through the Round-Robin thing.
You have to assign the IP to the first interface, then the second and then the third, and then see
if it works or not.
Otherwise, if you want to find out the easier way, you have to talk to your networking guy to find
out which cable or which port has which VLAN.
I'm sure every company would have a specific way of doing things.
Um.
Sometimes companies that I worked is very good in the documentation.
They actually have spreadsheet which would tell which port on the switch on the networks, which goes
to which port on the server because a server could have multiple ports.
So it will tell you exactly where that's going.
Also, if your networking team is not the ones that are doing all this work of running cables, then
you probably will have an install team or data center team that will perform all these tasks for you.
They are the one who will have that spreadsheet or the information.
They will tell you exactly which cable is going to which port and which port or which cable has which
VLAN side.
So check with them then check to see if you got the right subnet mask or gateway.
So if you do if config, you'll notice that your subnet mask for this interface, that mask is two five
five to four or five two five five zero.
OK, you're looking at it and you're like, OK, I had the gate, the subnet mask.
Then why I cannot connect to this IP address or why cannot I go from this machine to another machine?
Well, probably your subnet mask that is given to you is incorrect.
Maybe about two five five two five five two five four two five three, depending on how your network
is configured.
So again, confirm with your networking team that you got the correct subnet mask.
Now, please remember this whole scenario.
I'm talking about the static IP assignment.
If you are on the DCPI assignment, which is not static, then the your computer, your operating system
will pick up the correct net, must not mask itself.
You don't have to worry about it.
Also, it will pick up the gateway itself.
But in the static, uh, world, you do have to specify the mask and the gateway so that, as I said,
make sure you are given the correct that mask and correct gateway.
Now, how do you check the gateway?
The command that I use to check the gateway is not to stat space hyphen R and we this will tell me right
here the first line, first of all.
Right here, it's telling you these are the labels of the columns.
Then right here, the first column is telling you all the traffic, which is coming from whichever the
IP in this machine, which is that's why it's given zero zero zero zero.
All that traffic should go to the gateway 192 one sixty one point one.
And that gateway is telling it.
And all that traffic should be routed through the interface E and P zero s three.
That's how you see it.
And then you'll see right here all the traffic, a one to one sixty one 1.0 should go to this gateway,
which is eventually will route it to this gateway and then it should have a subnet mask of two five
four two five five two five.
For the last one you could ignore because I said this is for the bridge was a bridge adapter.
You could even disable that adapter if you want to.
But anyway, let's not get into this one.
I don't want to confuse you.
All right.
So make sure that the subnet mask and gateways.
Correct, then next thing is, if you think it is correct and it's given you by the network folks the
right gateway, then ping it to ping one to.
One sixty eight to one point one, if you are getting a response back, which is, say, 64 bytes and
you are getting the ICMP response back, it means the gateway is lessening and it is responding and
it is up this gateway in the real corporate world.
This is the IPSI most likely assigned it to the networking switch where all the computers are connected.
So you pinged it works.
Check if the gateway is assigned.
I just covered that by running the command net stat minus R and B.
If you do not see that gateway that is given to you assigned here, then you probably have incorrect
configuration in your configuration file.
And there is a configuration file.
It's an Etsy config, network scripts.
And if you do, if cfg ENP history, you'll see this is the static configuration file setting and this
will tell you right here how the configuration should be set up and if it's if it should have a gateway
in here as well.
Right now you don't see it because the type is set up for DCPI.
That is why you don't see it.
If you wanted to have a static, you will have to add it.
That gateway in the next one is check with the network team.
If the correct VLAN is assigned on the switch, there isn't any commands that you would have to run
for that you would basically have to pick up a phone or send an email to your network engineer and ask
them that you are on the correct vilan, then check their tool ethe tool or MMI tool.
I already covered that, but just go quickly, run it tool E and PS or three on your interface to check
the status of your interface.
If you want to know the speed of that, uh, port, if you want to know whether it's full duplex, have
to plug the link status, you will run that command.
The other command is M I dash tool ENP zero three and you will see E and P the type it correctly.
ENP on'em interface is correct, ENP zero as three.
Now you'll see here it says no order negotiation thousand, which is one gig of interface flow control
and lank is OK.
This is the same length.
OK, as if you see here is like detected.
Yes.
And the last one, if you are still trying everything, you can always try to reboot your machine or
you could just simply do system ctrl.
Our system control a restart network, and this will again go back to your configuration file, find
out if there are any issues.
If they are, it will notify you.
Check on the status of the neck by running if they come in.
We have covered that.
Also, we could check if it is up and down.
But looking at one specific thing that I was going to show you is, uh, right here.
It says ENP is three.
And you see what this is up.
It is not up.
Sometimes what happened is you probably do see that IP aside and everything is working and subnet mask
is correct.
But you don't see this little thing says up right here.
So in order for to for you to bring this up, then you can run the command if config E and P S3.
ENP zero, a three up, and then when you're done, if confirmed again, then you will see actually
this will come up as up and it will also second thing you have to check is it's running right here.
It's running as if you see here, it says up broadcast, but it is not running to make sure it is running
and then check to see if the IP is assigned to some other devices.
And the only way you could do that is if you go to another machine and paying that IP address that you're
trying to assign.
See if it exists.
But if it is tangible, then try to log into it and see if you are getting lending into the right machine
or not.
And the last one I said turn off the firewall.
This is one of the things that you could rule out by doing system.
CTL stop in the newer version is firewalled and the older version, it's services, a service IP table
stop and it is telling you since this is a newer version of operating system, is saying I'm redirecting
you to System CTL and in there you should use this.
Stop IP table service.
So if I use that.
I'm sure it is still exists, but it is deprecated.
Not loaded, meaning it is there, but it is not loaded, failed to stop because it's not up and running.
Why?
Because we have actually started running, firewalled.
Now it's a newer version that runs on in your S.O.S or RedHat operating system.
So these are the pretty much the steps that you need to take in the corporate environment.
And I am very, very sure very hopeful.
If you go through all these steps of troubleshooting the IP address when it is actually shows up, that
it is up and running, but somehow you cannot reach it.
That's what probably one of the reason I'm sure you will when you go through it, you will find it right
there.
Yes, that was one of the reasons.
And again, if you're still having an issue, I'm always here to help.
I'm always here to add more content to newer things to come in.