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<v ->Ping and traceroute.</v>
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In this video,
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we're going to cover the ping and traceroute command-line tools
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and how to use them in maintaining
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and troubleshooting our networks.
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First, we have ping,
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ping is used in checking the connectivity
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between two devices and we often use this
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in network troubleshooting.
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There are a couple of different ways to use ping,
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but the most common way is to just type in ping
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and the domain name you want to test.
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For example, if you're on a Windows machine,
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you can enter ping www.jasondion.com
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and hit Enter.
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And this is going to send out four pings
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and get four replies.
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And it tells you the site is either up or down.
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This is the default one that you're going to use.
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Now, if I wanted to get 10 or 20 or 30 pings,
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I can do that by doing ping -n and then the number.
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So ping -n 10 jasondion.com
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will ping jasondion.com 10 times, and then it will stop.
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Now, you can also do this
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where it will just keep pinging over
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and over and over again forever.
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To do this,
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you're going to use ping -t and the domain name.
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So in this example, I would do ping -t jasondion.com
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and it would go forever and ever keep pinging that site.
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Now, why would I want to do that?
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Well, it might be useful to see
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if your WAN link is up all the time.
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In some places I've worked,
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we've had a ping, constantly running on a distant end
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and we leave it up on a big screen monitor.
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Then we could just look up
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and we could see if that connection is working or not,
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or if it's having any issues.
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Now in the examples I just gave you,
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I was working on a Windows client,
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but ping does work a little differently
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if you're using Linux, Unix or OSX.
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One of the key differences, is that on a Windows machine,
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it only sends four pings by default and then it stops.
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If we wanted it to run forever,
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we'd use the -t option, like I said.
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Now, in Linux, Unix and OSX clients,
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ping is going to run continuously by default,
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just like that -t and Windows did.
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Now, if you only want to send four pings
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like we did in Windows,
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we would have to do that by doing the -c command,
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which stands for count.
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So it'd say -c 4 after my ping command.
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So I would do ping -c 4 jasondion.com.
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Or if I wanted to do 10, I could do ping -c 10 jasondion.com
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and then stop.
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Really, you can use any number
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of pings you want with the -c option
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and it works like the -n option you had in Windows.
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If you're running pin continuously on any operating system
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and you want to stop it at any time,
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you can issue the break command.
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To do this,
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you simply press the Control key and C,
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and this will end up breaking or stopping
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that continuously running ping.
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The last option we need to cover is the -6 option.
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If you enter ping -6 and the domain name,
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this is going to force the ping to go over IPv6,
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instead of IPv4.
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This -6 option is going to work the same
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regardless of the operating system you're using.
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So what does all this look like in the real world?
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Well, here you can see,
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I did a ping of jasondion.com from my Windows machine,
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and it sent out four pings and received four replies.
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Here you can see the time it took, 74 milliseconds,
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74 milliseconds, 156 milliseconds and 71 milliseconds.
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This gave me an average of 93 milliseconds
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across all four pings and all four pings were sent
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and all four packets will receive back.
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This indicates that my web server is up
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and accepting traffic at this time.
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Now, next, we have traceroute
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and this can be written
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as either traceroute all written out
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or tracert if you're on a Windows system.
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If you're on a Unix, Linux or OSX system,
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you're going to enter that command as traceroute.
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Now, either way, we pronounce it the same way,
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we call it traceroute.
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Now, traceroute is going to be used to display the path
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between your device and its destination,
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showing the source and destination IP address
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along every single hop as you go.
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Now, hop is simply any router or firewall
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that's there as part of the layer three path
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in that transmission,
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going from the client to the destination.
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To perform a traceroute,
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simply enter the traceroute and the IP address
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or domain name of the destination you want to reach
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from your client.
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Now in response,
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you're going to get a list of all the routers
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between you and the computer you're trying to get to.
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If you want to do this using IPv6, instead of IPv4,
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you can add the -6 option to your traceroute command.
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Now, let's look at quick example here
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by doing a traceroute to www.diontraining.com
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from my workstation.
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Notice, it's going to go out
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and resolve the IP address for us automatically.
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Then it starts tracing out the route
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from my computer with a source IP of 10.0.2.2
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out to the destination IP of 54.221.229.100.
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Now, how does traceroute work?
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Well, it's going to use the time to live field
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in the IP packet header.
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Normally, the TTL or time to live is going to be used
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to prevent packets from being forwarded
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around the internet indefinitely by routers.
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This would create a routing loop, right?
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So we don't want that to happen.
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Instead, each time a packet is forwarded by a router,
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it takes one off of that time to live.
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So if the time to live reaches zero,
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that packet is dropped and discarded
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and response gets sent back with an error message.
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So traceroute actually uses this to its advantage,
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and it sends out a series of packets to the destination.
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The first packet is going to be sent out
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with a time to live of one.
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It's going to hit that first router
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and then that's going to decrease it's time to live to zero
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because it hit zero, it's going to now drop the packet
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and send back an ICMP message
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that says,
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time exceeded for that packet back to the source IP
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and informs it,
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that that packet didn't make it to the final destination
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and it was dropped.
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Then traceroute sends out another packet.
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This time, it has a time to live of two.
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Again, it goes through the first router
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and it hits the second router.
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At that point, it's hit zero again.
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And so it's going to go back to the original sender.
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This continues over and over again
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until traceroute finally gets
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to the final destination successfully.
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But the entire time it keeps incrementing
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that time to live one, every time it sends out a new packet.
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This way,
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it can identify each and every router or hop
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along the source to destination.
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Now, sometimes you're going to come across something
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that looks a bit strange in your traceroutes output.
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For example, notice here around line 15,
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I have a bunch of timeout requests,
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even though my server is up and running.
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What does this mean?
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Well, this means you're seeing a firewall on our path
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or some other kind of device
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that's not responding to ICMP or ping traffic.
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This is a security feature of a lot of firewalls.
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So my traceroute command simply reports back
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that the response that it received
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or in this case didn't receive from that device at that hop.
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Now, this still tells me there's some kind of device there,
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but I know it's filtering that traffic.
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And so I'm now being able to fingerprint your network
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and figure out where your firewalls are.
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In this case,
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my service provider for diontraining.com does not respond
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to those types of request.
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Therefore, I can only trace the path
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as far out as the outermost layer of their network.
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Once I get to the outermost layer of their network,
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their border gateway,
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it's going to stop responding to my request
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and I'm going to receive timeout messages.
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But I won't be able to see all the information
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about the routers and firewalls there,
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except to know there is something there.
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And I can see that by those stars that are existing.
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Now, when it comes to troubleshooting your network,
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you can use ping to determine
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if you have a network connection
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from your source to your destination without any issues.
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If someone's complaining
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that their network connection isn't working,
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I usually follow a simple four-step process
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to determine where that issue is occurring.
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First, I'm going to try to ping google.com
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or some other really big website
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that's always up and available.
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If this works,
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I know my network connection is good
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and the internet connection is good.
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And in this case it would be a user issue
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that's specific to a website they're trying to access.
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If I can't ping google.com successfully,
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I'm going to switch to pinging an IP address,
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something like 8.8.8.8
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and I'll see if that works.
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Now, 8.8.8.8 is a great IP address to use
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for a couple of reasons.
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First, it's really easy to remember,
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it's just four eights.
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Second, it's the DNS server for Google.
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So it has an extremely high rate of availability
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and reliability.
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So it's almost always up and it makes a great IP to use
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for your troubleshooting.
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Now, if you can ping 8.8.8.8 successfully,
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this indicates your internet connection is working,
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but I'm probably having DNS issues
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because I couldn't resolve google.com
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to its proper IP address and ping it.
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At this point,
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we would shift our troubleshooting efforts
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towards the DNS issue either with our local DNS cache
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or our DNS server.
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Now, if you can't ping 8.8.8.8,
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this means you can't reach the internet successfully.
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So we need to go back and refocus our efforts
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by moving inwards by one step.
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Now, I'm going to ping my default gateway,
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my router or my modem.
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This way, I can see what the internal IP addresses
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of that border gateway router
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and see if I can reach it.
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For example, in my home office,
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we're using a private IP range of 192.168.1.0/24,
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so my default gateway is 192.168.1.1.
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If I can ping that IP address and it goes successfully,
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this means I have a good connection
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from my client all the way through my switches and routers
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up to that border gateway router.
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So now I can know the issues
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between my border gateway router
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and the 8.8.8.8 server,
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because something is wrong with our internet connection,
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maybe our modems offline or something like that.
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So we'll troubleshoot in that half of the network.
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Now, if I can't ping the default gateway,
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that means there's an issue between my client
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and my border gateway.
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This can be anything,
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it could be cabling or switches or anything else
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in between those two devices,
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including my local workstation itself.
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So the next thing I want to ping
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is my local client's IP address.
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For example,
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if your IP address is 192.168.1.23
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and your default gateway was 192.168.1.1,
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you're going to ping the local IP address
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of 192.168.1.23
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and you'll see if that works.
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If pinging that does work,
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this means that you have an issue
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between your network card and the default gateway.
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So you need to check your cabling and your switches
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and all the things outside of your device.
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Now, if you can't ping your local IP address,
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that means you now need to ping your local host
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of 127.0.0.1.
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If you can,
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that means your network card
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and its drivers are properly installed.
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If you can't,
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that means you need to re-install your network card drivers,
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because there's most likely something being corrupted
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in there.
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As you can see by just using my ping command,
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I can quickly identify where the issue is.
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Is it on the internet side?
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Is it a problem with my modem or my router?
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Or is it a cabling or switch issue?
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Or maybe it's a client or driver issue?
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By doing these four steps, you can figure it out.
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Now, if the issue is between the router and the destination,
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this is where traceroute is going to become really helpful
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for you,
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because I can identify all the routers are being used
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between my client and the destination.
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And then I can see where the data stops flowing.
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Then if I own that device,
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like an internal router or firewall,
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I can check its configuration
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and work to restore those services.
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(gentle music)