This is one of multiple videos discussing Dynamic Host Configuration Protocol or DGP and specifically
how to troubleshoot DHC.
In this typology we've got a client connected to a router connected to a DHP server and we've been told
that the client is not receiving IP addresses from the DHP server.
In this example rather than using physical PCs I've got us V-Rod is acting as DHP server and DHP client
so he has the client show IP interface brief noticed the client hasn't got an address assigned to Gigabit
00 DHB is being used but no address has been assigned so let's shut the interface down and then no shut
it to test.
What's happening.
Interfaces come up show IP interface brief interfaces up no address has been assigned through DHP.
So on the DHP server we're trying to debug a debug IP DHP server and I'm going to go for packets to
see detailed information.
We are already seeing something here says Cline's VPN is something no option 1 25 DHP discover received
from a client through a relay of 10 1 1 2 5 4.
So ADHD the message is being relayed by the router we can see in this example that router 2 has the
IP address on the interface facing the client that's the address that we see on the DHP server.
But we told her that option 1.5 is not present in the message.
There's a problem with option 1 25.
You can find information about option 125 in this RAFC vendor identifying vendor options for DHV the
problem here he said.
Option 1 25 is a vendor dependent.
So we've seen a lot of messages stating that option 1 25 is not present in the message.
So let's have a look at the relay agent show run interface gigabit 00.
Now we do see the IP help address on the relay agent which is routed to but we still seeing problems
on the DHP server we're getting information at the DHP server based on this configuration so we can
ping the DHP server.
DHP messages are being forwarded to the server but there's a problem on the DHP server.
So let's have a look at the DHV piece of a configuration.
We have a pool configured.
This looks right.
Network default gateway or default router that needs to be in the same subnet as the interface where
the client is configured.
So that looks right.
DNS server is 10 to one or two to one.
That is the IP address of the DHP server.
So that looks right there.
No excluded addresses in the pool.
So we've got a very basic pool and an IP address configured on the gigabit interface everything else
looks standard.
But I'm going to go through the shop run slowly to see if you can find the problem.
What is the issue in this configuration.
Post the video if you need to but there's a problem in this config.
Show IP DHV.
P Paul
we have a pool next address to be allocated to 10 1 1 3 shoyu IP DHP binding is an address allocated
to a client somewhere but no address has been allocated to this client.
Now this is something you need to remember for DHP.
Notice what happens when not top show IP route we are told that there's no gateway of last resort.
There's no writing on the DHP server.
The DHP server has to have a route back to the subnet of the relay agent brought it to is receiving
a DHP broadcast on gigabit 0 0.
But the DHB server doesn't know how to get back there.
So notice here it can't get to that subnet because it doesn't have a route in the writing table.
So IP route and I'll simply create a default route and point it to the IP address on Route 2 which is
gigabit to 0 1 so on the client show the interface brief and no IP address is allocated yet.
I'll force this by shutting the interface down and then shutting it show IP interface brief.
Let's see if we get an IP address in now and there we go.
We've just been allocated an IP address by the DHP server.
This address has been allocated to the client.
Now the reason that the binding was shown previously is that the address was allocated previously to
the client and then it broke the network.
So the same address has been allocated back to the client.
Now since we fixed the network so this is the thing about DHP service on Cisco.
Make sure that they have a route back to the client.
In other words they need to know how to get to the relay agent's IP address.
Otherwise they will not allocate addresses to clients.
So no we have a default route.
And if we look at the binding we should be able to paying the client.
And there you go making paying 10 1 1 2.
So that was an example of how to troubleshoot to DHP.
Don't forget that your DHB servers need Roths back to the relay agents in your typologies.
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channel.
I wish you all the very best.