Network Troubleshooting Tools - CompTIA A+ 220-702: 3.1

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There are many network troubleshooting tools available at the command line. In this video, you'll learn how to use tools such as ping, tracert, nslookup, netstat, and many others.

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Closed Caption:

welcome to this module of Professor
masters free comptia a+ certification
training course on network
troubleshooting tools i'm james master
and this module we're going to go
through the requirements from the
practical application exam which is 227
00 2 section 3 . one the troubleshooting
tools and most of them that are here are
command line tools that you'll use
whenever you're trying to find problems
that might be occurring on the network
we're going to step through each one of
these and by the end of this module
you'll know exactly the scenario you
should use whenever you should take
advantage of these and you'll also be
able to run these are the command line
yourself
let's start with one of the tools that
you'll probably end up using the most
whenever you start troubleshooting and
that's the ping command ping is
something that's used to send a request
to another device and if that device is
active it will send a response back to
that very much like a submarine sending
a ping out via sonar and getting a
response back from whatever happens to
be around it it's behind the scenes
really using a protocol called icmp and
it's using a function of that protocol
called an echo request what you're
hoping to get back as an echo reply this
is a management protocol that's built
into tcp/ip it's something that also you
can't always rely on not every device is
pingable not every device will respond
to a ping even if it is active so most
of this time what we're trying to do is
pick a device that normally we would
absolutely expect a response back from
that device let's try pinging a few
things around our network and see what
the response is here's my windows vista
workstation let's start pinging around
at some devices on my network i happen
to know on my network 192 . 168 that
zero . one is my router and if my router
is there I should get a response back so
it even says it's pinging 192 168 0 .
one and it's paying it with 32 bytes of
data so its senses 32 bytes out and what
we should expect as a response with
those 32 bytes and indeed we do we get a
reply with 32 bytes and took only two
milliseconds and a time to live number
of 64 that's a number that's used by
tcp/ip whenever these IP frames are
going out and they go through a router
that number will decrease by one and
it's a useful utility is useful function
of IP because if there happens to be a
loop in the network the time-to-live
will rapidly decrease all the way down
to zero and the next router that gets it
says sorry your time to live a zero and
it drops it so looking at this we know
that we can step through at least 64
different hops or routers until that it
tries to drop this particular frame
let's see what type of response would
get if we pick something out over the
Internet
I'm gonna paying a date that ate that
ate that is a google dns service that
they have and it's a great one to use
for troubleshooting internet
connectivity because eight that ate that
age should always be there
Google's very good about uptime let's
ping that and see what we get we get a
reply back from a date notice the time
to live a little bit smaller this time
instead of 64 we are now hopping through
quite a few hops to get 28 that a date
and back and you can see statistics at
the bottom we have zero percent loss now
if something wasn't on the network if I
ping 192 168 that zero . let's try 67
and see if 67 is there i happen to know
the 67 is not on my network in the
response we get back is the reply is the
destination host unreachable can't find
them can't get there doesn't exist
I'm not really able to access that
device so depending on your response
from a pain you'll know at that point
whether you're even able to communicate
out to that device or not and if you are
you can then continue your
troubleshooting if not you have some
other problems you have to deal with
first it was interesting that we had a
different time to live when we went out
to google to see what that device was at
eight
it will be interesting to know what were
the hops that that went through to get
all the way there and back on the
internet you may be stepping through
quite a number of different routers to
get to your final destination and then
it has to step through all of those
routers to get back to you and usually
they're quite a few different links
along the way the traceroute program
gives us some insight into that process
on just how many routers it has to go
through to get there let's do our trace
route 288 that a date and see what we
get
the traceroute command has a lot of
different functions available to it
let's just use the defaults trace route
which is abbreviated and windows to
trace RT and i'm going to go to eight
that a date and we'll just hit enter and
what we'll do is start so hopping
through different links along the way if
we get a response back from these
devices it will tell us how long it took
to get there if at any time it also is
at the end of this you'll notice there's
a bit of a delay sometimes it goes a
little faster as it tries to do a dns
lookup of the router and give you the
actual name of the router if you can't
find a name it waits until it times out
and then continues through with the next
one these columns are the response times
that we're getting for the trace route
which give us an idea of just how fast
or slow those particular Network links
are so to get 28 that 88 we've already
hopped through one of our 10 top now
notice we missed a response there on
that response time value sometimes that
does happen we lose packets on the
network on occasion and that may have
been the case there were already on hop
12 we're still working through the
network and you can see just to get to
that one server we've had to go through
123456789 10 11 12 and finally on the
thirteenth top we were able to get to
the google public dns and it was the dns
a at . google.com that's how far we got
along that way some of these routers
along the way did have a name associated
with them in a name service and it
actually put up here exactly on the
comcast.net network i went everywhere
from Tallahassee to Mobile Alabama to
dallas texas and then finally somewhere
along the line we weren't able to get
any names anymore and we finally got to
google and back so that topped all over
the southeast united states before it
ever got back to me and we were able to
see all of that with the traceroute
command if you recall when we did that
trace route at the end of the trace
route it said that we were connecting to
google dash public dash dns cache a .
google.com but I had typed in 88 @ 8
well this process of finding out the
name of a device or dirt for deriving
the IP address of the device based on
name is done through something called an
nslookup and you're able to go the
command line type in any name you'd like
and it should report back the IP address
of that device let's see what we can do
let's try some different names on the
internet and see what IP addresses we
get back we can run the nslookup command
right at the command line and let's do
an nslookup of eight that a date is
going to be a little bit confusing
because it's going to go to a google
public server and it's going to
restaurant respond back that it looked
up that address and it happens to be the
same server that we're using to do these
dns lookups what if we did an nslookup
of www.google.com that's a little bit
different we're doing it in reverse and
it's still going out to the google
public dns server to get this answer in
the answer that it gets back is to get
to wal . google.com we can go to any one
of these IP addresses you can see google
has a lot of different options for
connecting out to that Google server and
so your machine will pick one of these
dns updates and from that point on
whenever you type in google.com address
it just knows to always go to that IP
address
let's try another one let's nslookup and
let's go to www.cnn.com and see what the
IP addresses of CNN CNN again has a
number of different IP addresses and
there's a list there that we can also
choose from this is really what's
happening all the time behind the scenes
you go in a browser you type yahoo.com
behind-the-scenes the dns resolver
that's built into your operating system
goes out to whatever your default dns
server is like the 88 that a dedicated
google and asks hey Dino yahoo is and
that server responds back with a list of
IP addresses associated with that
webpage and that mean at that point your
computer ceases to know what yahoo.com
is it uses that IP address to
communicate back and forth if later in
the day you use that again you type in
yahoo.com has a local cache it remembers
oh yes I've already been there I've
already done the lookup for that now let
me just go to the IP address instead of
the yahoo dot com
it's a very very slick way to do this
very easy and you can always track back
what you're getting
based on that name or IP address using
the nslookup utility on your computer
there are constant network connection
being created being torn down that are
in process their number of network
connections that are waiting for people
to connect your machines that can
provide a list of the available shares
on your machine or a printer that might
be shared
there's many other things that we could
see behind-the-scenes by using the
netstat command because that's going to
list out for us all of the different
active connections and that are on our
machine some that are currently
established some that are waiting to be
established for able to view all of it
with that netstat command
let's start our netstat command i'm just
going to start typing nets that and hit
enter and what we're looking for is the
active connections that maybe on our
computer and it's gone through the list
of those and it knows that I just had a
web browser up and there was a
connection that was there already let's
start another web browsing session here
and behind-the-scenes well let that
build and do what it's doing and what I
would expect to see now is another list
of active connections that are on my
computer and what they happen to be
doing you can see the port numbers in
use and now you can see a couple of
others have popped up we can go to
yahoo.com we can bring up another tab
and go to google.com ago and we should
see active connections now building
based on these websites that we're going
to whether we are established to them or
whether they're open connections coming
back into us the netstat command has a
lot of command line parameters
associated with it you can really drill
down on some very specific information
here for the purposes of our a+
certification we just have to know about
the command and what it does but as you
can see there's a wealth of information
that you can / get out of the netstat
command if you know exactly what you're
looking for and trying to troubleshoot
whether you're able to make a connection
to a device or not the net command is
exclusively for Windows environment you
won't find the net command on a linux
machine or mac OS meant device this is
to provide us with interfacing too many
different functions that will allow us
to share the the microsoft windows
shares to start services to look for
other devices on the network other
computers on the network all using the
Microsoft protocols and you can see the
net command itself if we did a net just
by itself
look
the different options you have available
there's account information computer
information user information and we can
view different things on the network
let's try it out a command prompt
let's see this net command action i'm
just going to type net and hit enter and
you'll see that list of all of these
different things if i type net user and
we'll see the prompt here here's all of
the user accounts on Mike professor pc
computer here there's an administrator
account there's a guest account and
there's the professor account i do a net
accounts we go
you can see information about the
account configurations the minimum
password age the maximum passwords these
are all set to default because that's
what i've configured currently I haven't
changed any of the defaults in here so
all of these are very specific into how
your Windows Device communicates to
other windows devices using Microsoft's
own protocols and if you look through a
number of these you'll start to see
things like the ability to view all of
the available shares on a machine or the
ability to see everybody who's connected
to your device and when you're
troubleshooting microsoft problems that
can really come in handy at the command
line if you were to sit down in front of
a computer for the first time and you're
working on troubleshooting that device
you may want to know the local IP
address the IP address of the router
that this device connects to what dns
server is used by this computer to do
its name resolution you can view all of
those things in windows with the
ipconfig command and it will list out
for you everything associated with the
IP configuration of that device let's
run ipconfig on my machine here and you
can see my machine you can see the IP
address associated with it the subnet
mask the default gateway I can see I've
got other connections on here have one
adapter of another tunnel adapter
another tunnel adapter on here and those
are probably used behind the scenes for
VPN and other types of capabilities that
i've configured on here the one that
we're using is this local area
connection adapter and you can see
exactly the way that it's configure when
that was interesting to us but maybe
we'd like to see more information
i'm going to type ipconfig /all and hit
enter and a lot of things are going to
flow by so i'm going to scroll back up
to the top here to where i type this in
here
where i typed in ipconfig /all and it
tells you a lot more in this case it
tells you the hostname it tells you
information not only about the card that
you're using here but the mac address of
that device it is using dhcp to
automatically get an IP address we can
see the IP address that we've gotten in
we can also see things like the dhcp
server we got it from and we can also
see dns information so the / all really
shows you everything you would need and
now you can start troubleshooting this
from here can i pick my dns servers can
i pick those DHCP servers and worker
troubleshooting process out from there
if you're managing devices remotely on
the network you may find yourself
needing to log into those devices at a
command line and do some work on those
machines one of the programs you can use
to do this is called telnet which is
also the protocol that's used for this
application to work properly and allows
you in this console mode to connect to
an external device so that you can use
the keyboard and the command line of
that device to perform functions and do
the normal administration of that device
one thing to keep in mind is that telnet
is an unencrypted communication link you
don't generally see this used on
enterprise networks because you don't
want to log into routers and switches
which are extremely important
infrastructure devices and not have any
way to encrypt the data between you and
that device in those cases were doing
something called ssh or secure shell it
works exactly the same as tell that it
looks exactly the same as the tell that
might be but the link between you and
that device is an encrypted
communication normally have to check
that remote device and make sure that it
can support ssh or that you have the
ability to connect to that device via
ssh in enterprise environments most of
the time they are actually disabling the
ability to connect with telnet because
they don't even want in an opportunity
to connect to that device and not have
it encrypted almost all the devices
these days default to ssh and normally
everybody only turns on the links to be
encrypted using the ssh connection let's
review some of the things from this
module on network troubleshooting our
first question which troubleshooting
tool can determine the path of packet
takes through the network while we
watched a packet go all the way through
the network third
teen hops away to that name server and
it was the traceroute command that
allowed us to do that you can abbreviate
that at the command line and use it
trace RT as your command and the next
question which suite of commands
provides information about the windows
network while we were already using some
of that to view the users that were on
my machine and that was the microsoft
net command and the last question which
remote communication protocol provides a
secure connection between devices we
have the option of one that was not
encrypted and one that was encrypted and
that secure link was ssh or secure shell
that covers our requirements for r2 2702
section 3 . one where we've used a lot
of different tools here at the command
line to be able to help troubleshoot our
network links if you'd like to watch any
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