DHCP Failed. APIPA is being used.

SuburbanRythm · ‎04-14-2023

Hello,

I'm in a class for Cybersecurity and in our week 7 project I'm having issues setting up DHCP. I reached out to the instructor and received some feedback:

"You are having issues due to the server not being configured with appropriate IP settings, and the router interface not being configured. This will get you started. Ultimately you will need to review all of your settings for each device and interface. Always remember to work through each step one at a time. "

I am not understanding what is going on but the issue is that we are supposed to merge networks 1 and 2 (already done) and assure that all devices are within a Class C network (done on 1/2 (now Network A)).

I have attempted to set up DHCP on Network 3 but am failing miserably. I've been working on this for over 6 hours and cannot understand what I am missing. I was attempting to make Network 3 run off of IPs in the 192.168.6.xxx range. Server_Network 3 is the DHCP Server.

The two tasks that I have left are to use DHCP to auto assign IPs in Network 3 to a specified range in a Class C IP Range (I chose 192.168.6.xxx) and to be able to ping all units from any unit in either network. The units will ping within their network but not reach through from Network 3 to Network A or vice versa.

I am trying to learn, more than anything, what I'm doing wrong. If anyone could take a look and tell me what I'm missing or doing incorrectly, I would appreciate it.

Link to Cisco Packet Tracer File: https://drive.google.com/file/d/1u3lNtmIDfS5NdKVvNFBXrqXmfFpSCqoH/view?usp=share_link

Flavio Miranda · ‎04-15-2023

Hello,

Find attached a file with DHCP working.

A few thing I´d like to point out:

The DHCP server connected direct to a router is not usuall but it is not wrong. But we usually connect server to a switch, just a comment.

- The DHCP had the gateway wrongly configured. You put ip address 192.168.6.1 on the router interface and left the DHCP server with gateway in another network. The default gateway for DHCP server must be the router interface.

- When you plug a layer 2 switch into a router you better use trunk. On the router side you use encapsulation do1q and use the vlan id you create on the switch. On my case I used 10 in one side and 5 in the other side.

- Serial links had different IP on different sides. You need to put both on the same network otherwise there will be no communication.

-When using dynamic routing protocol like RIP or EIGRP you need to advertise the network by using the command network and the network connected to the routers.

- If you want to serve two different networks with the same DHCP server you need to create mote than one DHCP scope on the server.

If you have any doubt just let us know.

SuburbanRythm · ‎04-15-2023

Thank you so much for all the notes! I do have more questions.

1. When you say the DHCP Server must be the router interface, do you mean the DHCP server (IP) must be the outgoing to the network that is requesting DHCP?

2a. "When you plug a layer 2 switch into ... use trunk"
- I thought that trunk was primarily used for VoIP connections. What is the purpose in layman's terms?

2b. "use encapsulation do1q and use the vlan id you create on the switch"
- I will have to learn, but I have no idea what do1q encapsulation is. I also thought that the VLAN IDs were set to 1 which is default. As the entire network was set to 1, wouldn't that make it easier for all units to connect? My thought was that if they're on the same forest (terminology?) then they should be on the same VLAN. Is making a new VLAN better for organization or does it just work better?

3. "serial links ... the same network otherwise there will be no communication"
- Thank you. I did not know this. Honestly, I'm having some imposter syndrome. I'm in these classes but sometimes I feel like I missed a step in learning, or was simply not taught what I'm supposed to do. I reached out to some peers who feel the same way. Thank you so much for telling me.

4. "when using dynamic routing ... need to advertise the network"
- Can you elaborate further on what this means? I have not heard of advertising the network.

5. "create more than one DHCP scope"
- You mean that both Network A and Network 3 are requesting DHCP from Server Network 3... as such, the networks need their own respective IPs set in the DHCP scope, right?

6. The DNS Server is set to 192.168.10.1, but where in the network is that directing to?

Thank you so much again for the tips and pointing out my mistakes. I reached out to the instructor in between and the response was that I just further complicated the system with some relatively vague detail. I had no idea where to begin.

Flavio Miranda · ‎04-16-2023

I will.comment your question:

"1. When you say the DHCP Server must be the router interface, do you mean the DHCP server (IP) must be the outgoing to the network that is requesting DHCP?

"

What I meant is that the Server must be on the same network as the router interface. If the router interface is 192.168.6.1 the Server must be 192.168.6.x. Thats it. They must be on the same network.

2a. "When you plug a layer 2 switch into ... use trunk"
- I thought that trunk was primarily used for VoIP connections. What is the purpose in layman's terms?

Trunk is necessary to tag the packets. You can see that on the routers interface I added something like

dot1q right? This is to tell the router that the traffic coming through that interface will be tagged and from vlan 5. It could be any vlan number.

This way switch and router can understand each other. And if you need one more vlan, you just need to create a new sub interface on router and map the new vlan.

2b. "use encapsulation do1q and use the vlan id you create on the switch"
- I will have to learn, but I have no idea what do1q encapsulation is. I also thought that the VLAN IDs were set to 1 which is default. As the entire network was set to 1, wouldn't that make it easier for all units to connect? My thought was that if they're on the same forest (terminology?) then they should be on the same VLAN. Is making a new VLAN better for organization or does it just work better?

it could be. The dot1q I explained above but vlan 1 is the default vlan. It is a good practice not use it.

Dot1q is the same as trunk for router.

3. "serial links ... the same network otherwise there will be no communication"
- Thank you. I did not know this. Honestly, I'm having some imposter syndrome. I'm in these classes but sometimes I feel like I missed a step in learning, or was simply not taught what I'm supposed to do. I reached out to some peers who feel the same way. Thank you so much for telling me.

4. "when using dynamic routing ... need to advertise the network"
- Can you elaborate further on what this means? I have not heard of advertising the network.

You actually used it but the network must be the ones connected to the router.

5. "create more than one DHCP scope"
- You mean that both Network A and Network 3 are requesting DHCP from Server Network 3... as such, the networks need their own respective IPs set in the DHCP scope, right?

You could use only one dhcp scope but then you would create a problem because hosts from both sides would have the same network address and router wouldnt know how to send packets from one side to another.

If you have different network segment, you need to use different ip address and this means different scopes.

6. The DNS Server is set to 192.168.10.1, but where in the network is that directing to?

the DNS must be informed by DHCP server to the host. But DNS only make sense for web

Thank you so much again for the tips and pointing out my mistakes. I reached out to the instructor in between and the response was that I just further complicated the system with some relatively vague detail. I had no idea where to begin.

You are welcome.

You put a lot of network concept together but that they way to go.