In this video,
we're going to discuss IP settings.
This can occur when you have the incorrect IP address,
subnet mask, gateway, or DNS server IP address
assigned to a client,
and it'll cause issues for you with your IP settings.
Remember the fact that every network client
needs four key pieces of information
in order to communicate properly on the network.
This is their IP address, their subnet mask,
the IP of their default gateway,
and the IP of their DNS server.
Now let's take a look at a static assignment
on this OS X client.
Notice here we have three key pieces of information shown,
the IP address, the subnet mask,
and the router or default gateway.
The DNS server IP is on a different tab
and it really doesn't matter for this example
as long as we don't need to conduct name resolutions.
So you are called to troubleshoot this client
because they can't access the internet.
Let's assume you already tried to ping the server
at 8.8.8.8, and it failed.
So you know you have some kind of a routing issue here.
What could the problem be?
Now, I want you to go ahead and pause the video here
and look at it and see if you can figure out the issue.
All right, I'm going to count to five.
One, two, three, four, five.
All right, you're back.
Did you figure out the issue?
In this case,
the issue is that we have the wrong default gateway.
Notice the IP address is 192.168.1.200
and it has a subnet mask of 255.255.255.0.
With this subnet mask,
the default gateway would have to be an IP
of 192.168.1. something
because it's in this 192.168.1.0/24 network
for us to be able to reach it.
Now, if the default gateway is set at 10.0.1.1,
and this is truly the IP of my router,
then I have an incorrect IP address
because again my subnet mask of 255.255.255.0
if applied to the router's IP address of 10.0.1.1
would tell me I need to have something in the network
of 10.0.1.0/24.
So to get this client to connect to the internet
and have its traffic properly routed,
I need to change either the default gateway to 192.168.1.1
or change the IP address to 10.0.1.200
or something like that.
All right, let's take a look at another example.
This one comes from a Windows client.
Just like our last example,
this client cannot ping 8.8.8.8 successfully.
So you see the client has a statically assigned
IP address of 192.168.1.200.
Its subnet mask is 255.255.255.128.
And the default gateway here is 192.168.1.1.
All right, go ahead and pause the video.
I want to see if you can identify the issue
and think about how you're going to fix
this client's network connectivity issues.
Pause the video and come back
in one, two, three, four, five.
All right, you're back. Did you figure this one out?
Let's take a closer look at that subnet mask.
Notice it wasn't a classful Class C of 255.255.255.0.
So this isn't the 192.168.1.0/24 network
and it doesn't have 254 usable IP addresses.
Instead, we have a subnet mask of 255.255.255.128.
This gives us a /25 network using CIDR notation.
That means we only have 126 usable IP addresses.
So if our gateway is 192.168.1.1
and we have a subnet mask of 255.255.255.128
then our network IP is 192.168.1.0
and our broadcast is going to be 192.168.1.127.
Everything between those two ranges
is going to be usable IPs,
but our client was assigned 192.168.1.200
and that means it's assigned into a range
that's in another network,
so that IP address and gateway aren't on the same subnet.
This would explain why we can't route our traffic
to the network because we can't reach our default gateway.
This is going to be a problem for us.
So our solution would be to change our IP address
to something on the same subnet as that default gateway,
like 192.168.1.100,
or we could see if there's a gateway
on the same subnet as our client.
This means we need a gateway with an IP address
of 192.168.1.129 or something between there
and 192.168.1.254
because our network IP will be 192.168.1.128
and the broadcast will be 192.168.1.255
if we're using the subnet mask for a /25 network
of 255.255.255.128.
All right.
Now if you're going to connect to a website
by its domain name and that isn't working,
we need to look at the DNS IP server configuration.
In this case, you'd want to ensure
you have a working DNS server
and the IP has been properly entered on the client.
If you don't have your own DNS server,
you can always set your DNS server's IP to 8.8.8.8
which is the public DNS server hosted by Google.
So here you can see the DNS server
is set to 192.168.1.1 as the primary
and 192.168.1.2 as the secondary.
This is fine as long as the DNS servers there
are running on those IP addresses.
Now, if you don't have DNS servers,
then you want to reconfigure those to the public DNS servers
at 8.8.8.8 and 8.8.4.4.
Both of those are Google's DNS servers.