- [Instructor] Going back to my favorite router here,
the corp router, I'm going to go ahead and log in.
I'm not going to log in very far.
Cause what I'm gonna show you is
that I'm going to do some commands from user mode.
Now, you can type in show question mark
and see all the commands
that will give you a powerful output,
enable you to troubleshoot and verify your network.
In this case here, I want to do some of my basic commands
that I've been using for a while.
Show ip interface brief,
which I want you to be very familiar with,
and a show protocols,
basically the same thing but gives us our mask.
But there's some other commands here we haven't run through.
Show ip protocols, okay,
and this is going to give me my routing protocols
that are configured on my router, in this case rip.
And we'll go through this output in detail later.
But this is the routing protocols
that build the maps of my network.
And then to see the maps of my network, show ip route.
This is my routing table,
that the routing protocols built.
Along with my directly connected networks are in here.
And again, all of the output from these commands
will be discussed in detail later.
But very powerful commands,
lots of great show commands you can use.
The next thing I want to do is talk about the ping command.
As you know, I can ping the neighbor router
using it's ip address.
I can ping the neighbor router using it's host name.
But one of the things I can do that I haven't shown you yet
is I can type ping enter.
And this is gonna be my extended commands.
Notice that I need to be in privilege mode
to run what's called the extended ping.
I can ping from user mode,
but if I want to do something called extended ping,
and change the variables,
I can change the protocol for example,
I would need to be in privilege mode.
So, protocol is ip is fine,
let's go through some of these target ip.
172, 16, 10, dot two is San Francisco.
One of the reasons I would do this is,
say, I want the repeat cap
to be 50 instead of five, or 500.
Also, the datagram size, I want to test the mtu,
maximum transmission unit,
by changing it to a higher number.
Time out, and extended commands,
some of the things I'm gonna use
because I want to change my source address,
where it's coming from.
So, instead of saying coming from
my directly connected interface,
I want to choose a farther away interface on my router.
Alright, check this out.
So, that's the corporate LAN,
and by doing that that's going to route it
through my router,
instead of just being directly connected
and not use the routing.
In this case, here now I need to route
to ping to that directly connected interface.
There it says, you'll just say no.
And then, and now I just pinged.
And I route it through my router to do that,
that's an extended ping.
And the reason you would do this
is to change your source interface, to test your routing,
to make your repeat count higher,
or your datagram size larger.
And the last command that I'm gonna use
is the trace, you can just use trace, it's trace route.
Every device in the world except windows uses trace,
or trace route, right?
So, I can do this, trace route San Francisco,
and I'm directly connected,
so I could do an extended trace.
I don't usually use this too much,
but, 16 dot 10 dot two,
and notice that it's asking my source address.
So, now I can route to this, right?
That's kinda nice.
And then I'm just gonna go ahead
and go through all these and let it go.
Now, notice the time to live,
trace route uses the time to live field
in the ip header to find the path
that a packet takes to get to a remote device.
In contrast, a ping that just tells if the host is alive,
this will tell us the path a packet takes
to get to that device.
By using time to live, time out,
so in other words I set my time to live of one,
and that's what I did here.
And when it gets there, the packet dies
and then the router says hey, your packet died,
here's where the body of the packet is,
and comes back and tells us that hop.
So, if I had further hops it would just keep going here.
Now, the best test, one last thing,
the best test is to use an application layer protocol.
So, just because I can ping and trace route to a device,
doesn't mean my network is working perfectly.
So, I want to do an application.
In this case here I'll just telnet San Francisco,
and we'll see that this works.
And now I'm at layer 7,
I promise you I do not have a network problem
between me and San Francisco router
because I just did a layer 7 telnet protocol
over to layer 7 on the remote device.
You do not have a network problem.
Now, that's not the same thing as if you use ping or trace
that'll tell you if you're working up to the network layer.
This tells me that I'm working up to the application layer.
So, we can see by using some show commands: ping, trace,
and then a layer 7 protocol,
we can quickly verify and troubleshoot our networks.