- [Instructor] Alright guys.
Now that we've configured a simple DHP server
on the Corp router for the clients off the LAN port,
directly connecting made it very simple.
But if we have a scenario like this where
I'm looking at the San Francisco router
and there's a LAN on the
other side of the router 192.168.10.0.,
those clients are gonna send a boot p port 67 DSP request,
It's gonna go to the S00 and it's gonna be discarded.
So we need to be able to set a relay
on that interface to say hey that's not a bad broadcast,
let's change that to a unicast,
put a destination IP under sent,
and send it to the Corp router
to get an address for my DHP servers.
Alright very common configuration we do on today's networks.
Let's go ahead and take a look at the Corp network
and build a pool for the San Francisco LAN.
Alright so I'm gonna log in here.
First thing I'm gonna do is show run,
and let's take a look at our DHCP include DHCP there we go.
Alright we can see our Corp LAN there on the address there
so I'm gonna go ahead and say config T
and the first thing guys, what do you do?
Create a pool and some addresses, no.
Say IP DHCP excluded addresses right?
192.168.10.1, make sure you get rid of
the addresses you don't want to hand out.
I'm just gonna drop two right now.
Okay so we got our excluded addresses gone,
so I can go ahead and create the pool name.
Okay, so -- and then create my network.
Okay so I have my network
and it's gonna start heading them out.
I do have my debugging on, that's why it's sending those
because I wanted to see more information
as I built the pool this time.
So I'll show you those debug commands in a minute.
DNS Server for example, whatever.
And the other one, minimum default gateway router
or default router is the command, 192.168.10.1.
Okay, so, we put that in, and again I can do
do, show, run, include DCHP.
And it didn't like that cause I spelled it wrong.
Okay and then so we can see our information,
we have a San Francisco LAN in our pool.
Now there's something else I wanted to show you.
We're still in the config for the San Francisco LAN
and there's two commands for the CCNA objectives,
did I say that louder? Yes (laughs) for the CCNA objectives.
The DHCP lease is 24 hours by default.
We can set it to infinity,
and I highly recommend not doing that,
but you could set something like
oh I want it three days, 12 hours, and one minute.
Whatever the last one is, so it's days, hours, minutes.
Set it to whatever you want,
I just need to explain that to you
so if you see it on your CCNA objectives.
The next one is something called option.
So we got option and the one for the CCNA objective,
is option 66, which defines a TFTP server.
So we're going to hand out a THP server for example
this is used if you have an IP phone.
So I'm gonna say it's an ascii text,
and it's at tftp.lammle.com, and so a tee -- a VOIP phone
will come up and say I need a THP server,
and we'll be able to hand that out
via our DHCP server to the San Francisco LAN
cause that's where this is at.
Okay so now I'm handing out option 66,
which hands out a location of a THP server, so for example
a phone can download an operating system.
Alright we are done here now let's go ahead
and telnet out to the San Francisco router,
and I can do that by just doing SF since we set up our names
and I'm now in the San Francisco router.
Now, very simple guys, I can just put the relay
on the interface, let's take a look at that one more time.
Put the relay on the interface
which is F00, which one is going
to receive the broadcast F00?
One command, easy, and my host will start
getting DHP addresses off the Corp router, now,
I'm going to tell the relay to make a unicast,
take that broadcast, make it a unicast
meaning it has a destination IP address
and send it to the Corp router,
which we're directly connected to as 172.16.10.1.
We can use any IP address of the Corp router,
but we'll just use the one we're directly connected to.
So I'm gonna config T, interface F00, IP helper address,
172.16.10.1, my DHP request will now be fowarded.
Now, the other thing you need to remember about this command
is be careful, research it before you put it out,
it does forward more than just the DHP request.
Alright let's log into the switch,
this is the switch of the San Francisco LAN,
and I'm gonna go enable interface VLAN
which is my logical interface where we do our management
on our Cisco switches by default.
I have DHCP logging turned on as well,
that's just why we're seeing some DHCP syslogs here.
IP address DHCP, and that's not gonna work
until I enable the logical interface on switches,
or disable by default.
So we can see and watch this come up
because I have my debugging on,
and there's my interface (chuckles) that worked great guys.
My corporate router is the DHP server,
the relay worked, the IP helper address worked.
Let's run back.
Okay now that I have an IP address on my switch
let's run back to the Corp router
and we can see that I had DHCP debugging on.
So can see there's a DHCP offer, there's a reply.
I can't see everything on here
but I can also see there was a reply
to the relay 192.168.10.1.
So this is a great way--and let me show you what I turned on
I said debug IP DHCP server, I think I used events here
and or packets, or packet I usually use both.
But this is going to help you troubleshoot,
and find out why you are or are not
receiving an IP address from the server.