This is one of multiple videos discussing Dynamic Host Configuration Protocol or DHC.
This is a DHP trouble shooting video.
We've been told that the client on the left in the apology is not receiving IP addresses from the DHP
server on the right.
So let's investigate what's happening.
So here's the client I'm using an Iowas Virata to mimic a client in this Janissary typology show IP
interface brief.
We have a gigabit 00 configured for DHP but the interface is currently administratively down.
So lets enable that interface show IP interface brief interfaces.
Now up up as we can see here but at the moment we are not receiving an IP address from the DHP server.
This road is acting as the DHP server so show IP DHP pool allows us to see that a DGP pool is configured
on this Rodda with the name PC pool there are 254 addresses configured in the pool in this range.
No addresses have been least at the moment show IP DHP binding.
So shows us that no addresses have been least to any devices so D-bag IP DHP server packet.
Let's have a look in real time what's happening.
The client still doesn't have an address.
So what I'll do is shut the interface down and then no shut it to see if that makes any difference.
So the interface comes up.
But notice we see no output on the DHP server.
In addition to using CLIA commands.
What I'm going to do here is use white shark and capture traffic on the link between the client and
the router to see if DHP requests are being sent.
So notice we do see a DHP discover it's coming from a device with no IP address and it's going to broadcast
of 4:35 five to four five the source port is UDP or use a datagram protocol port 68 destination 67.
This is the bootstrap protocol.
In other words it's a DHP discover message.
The client is trying to discover a DHP server on the network.
In additional Stata y shot capture on the site to see if any DHP messages are received on the server
side set back on the client.
I'll shut the interface down
oh no shut it.
And let's see if we see any DHP traffic on the server side server side is seeing no traffic at all.
But the client site is seeing DHP discover messages and there are quite a few of them.
Now and why is shocked if you full to full DGP it doesn't work.
So you need to full to boot.
So use Boot P rather than DHP when filtering for messages we see a lot of DHP discover messages on the
client side but none on the server side.
So it looks like the DHP discover message is hitting the router but is not being sent to the server.
Now notice the type of message used.
This is a broadcast a broadcast is not forwarded by a broader or lazy switch.
Something needs to be configured on the router to able that traffic to be sent to the server.
So show run interface gigabit 00 can you find the problem.
I've given you a few hints.
Once again DHP messages are being received by the router but they not being sent to the DHP server.
What's missing in this configuration OK so DGP messages are dropped by the router because they broadcast
messages unless you enable the IP help address command so we need to enable the IP help address and
then send the traffic to the DHP server.
Now this typology the DHB server has the same IP address.
So we need to configure the IP help address on Rodda too and pointed to the DHP server.
Now that I've done that let's see if DHP messages are forwarded to the server.
And notice without doing anything else we can now see the DHP discover this is between the Rodda and
the server full to boot.
Notice there's the Discover message from 10 1 1 2 5 4 to 10 1 to 1 not 2 5 4 is Rodda to
notice the Discover message was forwarded to the DHP server for a client with the name client.
In other words Rato one acting as the client.
You can see in the output here that the broader received an IP address from the DHP server and you can
see that here as well.
So this is the DHP discover forwarded to the server the servers then replying back to the Rodda with
the not for saying that this is the service IP address list time is one day default gateway or default
grottos 10 1 1 2 5 4.
The client is requesting the address.
So is why Shaw captures on the right hand side of this typology.
So the client would have sent that message to the router and the router is now forwarding that message
to the server.
We can see that by looking at the Y shall capture here.
Here's the offer from the server to the client.
And he has the client sending a broadcast requesting the address brought costs and not forwarded by
the broader the client is requesting the address from the DHP server.
The DGP survey acknowledges that and gives the client the address 10 1 1 2.
So previously the address that was offered to the client was 10 1 1 2 and that was given to the relay
agent 10 1 1 2 5 4 in other words the broader
the client is requesting that address and the DHP of acknowledges that.
So hence the client will rot.
One is given this IP address and if we look at the writing table it's been allocated 10 1 1 2 5 4 as
its default gateway and that's because on the DHB server and notice we can see all the debugs showing
you DHB discover DHP request and so forth.
DHP server has been configured
with this configuration client is being allocated an address in this range.
Default Rodda is 10 1 1 2 4 4 DNS server is 10 1 to 1 which is the DHP server.
So that was an example of how to troubleshoot Dynamic Host Configuration Protocol or DHV.
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