Testing Network Connectivity

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Welcome back. Here we are in our first lesson on testing network connectivity.
Our objectives for this lesson include taking a look at some command line utilities like I P Config,
Ping Trace Route and Telnet.
First, let's take a look at I p. Config. This stands for Internet protocol configuration.
This is going to display our network configuration on our local system.
We can also use it to release in renewed DHC P addresses.
G eight CP dresses are assigned by a central server or networking device to nodes or systems that are connected on the same network.
Running I p config by itself will display the I P address, submit mask and the default Gateway.
And if you add slash all afterwards, it's gonna display more information such as the physical or Mac address, and the D. H C P server is connecting to.
We'll see some more options when we take a look at this inside of our demo.
Next up is the Ping utility. This tests and activity to another computer network device or even a website. It uses thebe TCP slash ip protocol and also uses Internet control message protocol, or ICMP packets,
and it sends these packets to the network device or host and waits to get a response back.
It also calculates if any packet loss has occurred and the average round trip time to determine Layton Z to the host.
Next step. We have trace route,
whereas Ping will just go to the final host or destination and wait for a response.
Trace Route checks every network device or router along the route to the destination and displays it.
It also uses ICMP packets, and we'll test the destination with three tests or probes.
It also calculates the time to live or t TL or the round trip time to that network hop.
And finally, we have telnet. This is a protocol that we use to interact with Roe computers, and we can use it to test and create a TCP connection to the host on a specific port.
Once the session is established, you can use it to interact with the remote system.
For example, you can tell net to an email server and actually create and sending email using telnet commands,
and you can see on our screen shot where I've tell mated to this I P address over port 25.
If you look at this inside of a window system, the Telnet client isn't there by default and typically requires installing it as it's an additional feature of Windows that does it for the basics of our commands that we're gonna learn in this lesson. Let's jump over to our workstation and test them out.
Here we are on our Windows 10 workstation named W S 01 In first, we need to open the command prompt.
If you've never opened it before, you can click on start search for command problem
and open it from the list of applications that finds
now. I already have a session opened, so let's go ahead and switch over to it
first. Let's take a look at our local I p configuration using the I P config command running. Just I Pekan fake will get back our I P address, Submit mask and default Gateway.
You can see here r I p addresses 169 dot to 54.40 at 201
Now the 169 dot to 54 address is an EpiPen address which stands for automatic private I P address.
This is the I p address you get if you do not get one from a d h c p server.
So if you see this, that means your system is either not on the network. Or maybe the D H c P server is having an issue, and you are unable to get an address from it.
If you think the network issue has been resolved or the D H. C P server is back online, you can run i p config slash renew
an attempt to get a new I P address.
Now, in my environment, I don't have a d h c p server to get an I P address from, so I'm not going to run this as it's just going to time out.
But just know if you're on the network and you're not getting an I P address from your d. C. P server, you can't attempt to get a new one by running slash renew with the I P Config command.
Instead, I'm going to open the network connection control panel and go sign a static I p address. I get there quickly from the command prompt by running in CPI a dot CPL
and here I have my Ethernet network adapter
minute to right, click on it
and choose properties
going to go to Internet Protocol, Version four, option here and select properties
and you can see it's already set to obtain an I P address automatically, which is what you would do if you want to get an I P address from the D. H C P server.
Instead, I'm going to check this radio button here to use the falling I P address
and I'm going to set a static I p address for the system.
Let's go ahead and click on OK,
Let's go back to our command. Prompt.
I'm going to up arrow inside the command prompt to get back to my previous command. Let's run i p config again and I've got my new statically assigned I P address.
Now, if you want to see more information about your network card or network information you received, you can run I p config slash All
here. You can see we get a description of the network device, the physical or Mac address of it if we have d HCP enabled
as well as our DNS servers.
So just by running all you can get a little bit more information, including R. I. P V six address.
Let's go ahead and clear this screen
now there were on the network. Let's test connectivity to some other devices
for this. We're going to use the ping utility
now. One thing you can do with the Ping Command is test and verify that your own TCP I p. Stack is working by pinging your local address of 1 27.0 dot 0.1.
If you get replies back, this manger local coal network configuration is up and running correctly.
I personally have never seen this failed, but it's always a good thing to test if you're running into some weird network configuration issues.
Now we just configured our static I P address with our default gateways. Let's see if we can ping get and have connectivity to it,
and that looks good as well. We got four replies back from our gateway and is relatively nearby, with a round trip time of less than one millisecond. Now, in addition to testing network connectivity to network devices, you can also test things like host names or websites. Let's go ahead and try a website here.
We're going to paying google dot com and we get a reply back. We see the round trip time is a little bit bigger, but again, we were sent four packets and we got back. So we're not losing any packets along this network path, so it's really good to see
one thing to note is not all host or network devices allow. Replying back to ICMP packets,
for example, the default Windows firewall actually blocks them. So if you ever try to ping a Windows host that she knows on the network and don't get a response back, But you know the servers up and running. One thing to definitely check is the local firewall.
For example, we just pained google dot com. Let's try another website
and we'd see we got an I P address.
But our request are starting to time out.
This means that being dot com is not going to respond to our ping requests, but I do know the website is up and running. Could easily open a rep browser and go visit it and you can see down. Here are it's statist. Exchange it a little bit as well we sent four packets, but we didn't receive any back, so we had 100% packet loss.
The default Ping Command will just send four packets. You can't increase this if you want, but one thing I typically do is add the Dashti parameter.
This is going to continue pinging the remote host and getting back
responses until you break the command using control. See,
this is really good. If you're may be waiting for a device to reboot and you want to see when it comes back up, or you just want to get statistics over a period of time to see if there is intermittent network connectivity issues going on.
For example, let's jump back over to the network connections.
I'm going to disable my network card
and we start getting failures.
If we enable it again
and go back to our window,
we'll start getting responses back
so you can see this is again really good, too.
Test connectivity to remote host and see if you have consistent connectivity to it
in a press control, See to break the command
and you can see we actually had 20% packet loss when we disabled the network card.
It's good and clear this screen again
now. So far we've verified our local I. P configuration is up and running and we're on the network, and we tested connectivity to a single remote host.
But what if you're having intermittent issues connecting to a remote host and you want to see everything in the path to that host
as you suspect, something else is causing an issue there.
For that, we can use the trace route command.
Let's go ahead and run a trace route out to our WiFi router that we saw in the last lesson. That's our last top. Before we go out to the Internet,
we're gonna start seeing results from the three probes that we're sending out.
1 72.16 dot three of that one is our default gateway, which makes sense. It's the next top in our network path,
and here we see a couple Asterix or stars. That just means the router did not return our expired. Time to live value,
and you'll see that occasionally not everything is going to give a response back in the path,
but it's going to continue and we'll get responses later down the network connection.
And finally, our third hop. There is our WiFi router.
Let's run trace route back for our website so we could get a little bit more information
again. We're gonna hit the default gateway and
follow the path outside my local network.
And now these tin 0.9 and 100.1 26 are going out through my local Internet service for Ryder
and you can see occasionally the trace route Command will also perform name resolution against I P addresses and give us actual host names. Here, you can see host names of some routers and you can see my I S P is Cox Communications.
Finally, once it gets out to the public Internet, we're going to finish up here and get our final response back from the Google Server
and you can see in this trace route results. We had two times where we had requests timed out, but again, not to worry. It's just gonna continue along the path and give us a much information as they can
Now, I mentioned trace route here is performing some I p address name resolution to give us actual host names. But if you didn't care about that and wanted just I p addresses. You can add the dash d parameter
and have it not performed DNS lookups
and a quick correction there. The Dash D needs to come before the host name
You can see this time we just got back I p addresses. We did not get the names of some of those devices back if it was able to perform the name resolution.
Let's go ahead and clear the screen again.
Finally, let's take a look at Tel. Net. We're going to use this to create a connection to a remote system over TCP
to a specific host name or I P address and pork combination.
Remember, we do have our server, 01 system inside this demo network. Let's go ahead and try to tell Mitt to it over Port 25 which is used for email services.
And once we make thes successful connection, we have a prompt here where we can actually interact with that remote system.
Like I mentioned in the slides, you can actually use Telnet to create email messages and send them to and from a server.
Now this session would eventually time out, but If you need to break out of it, you can do control, plus a right bracket.
And when you get to this interactive, prompt type, quit.
I'm going to use the up arrow to bring back our previous command.
Also have a Web server running on this remote server, So let's go ahead and try poor 80.
You see, we also made a successful connection, but there's no system for us to really interact with, so we just get a blank line here with the cursor. That's OK. That means we still made a successful connection to that remote server over poor 80.
So we verified we can make a remote TCP connection to that server over that specific port.
Let's go ahead and break out of this telnet session as well.
Let's try a different port that I know we're not gonna be able to connect to, so you can see what a failure looks like. It's going to attempt to make the connection,
and it's gonna come back and say it couldn't open a connection to the host on that specific port. So if you know something is up for running that can respond back to a TCP connection. You can use the Telenet Command to verify if you can connect to it and make that TCP connection.
If I knew these server was up and running and Port 80 was available, that's hosting our website. But my connection failed. That would point me to something between the two system is causing an issue could be a host level firewall or a network firewall that's blocking the connection. At that point, you can then use the trace Route Command to find everything between the two
and start investigating each of those systems
that does it for a demo. Let's jump back to the slides and wrap this up.
Coming back for our demo. I've got a quick quiz question for you. What command is used to get a new D HCP address
and the answer is I p config slash renew
That does it for this lesson. In this video, we discussed
how we couldn't verify our network configuration
how we can test connectivity with the ping utility.
We verify our network path using the trace route command
and finally, how we can test host and poor connections using Tell net
coming up next, we're gonna take a look at a very important subject of how we contest domain name resolution.
See you in the next episode.
Up Next
Testing Name Resolution
Advanced Networking Tools
Capturing Network Traffic
Troubleshoot Network Devices