Need help with Vlan switching & Ospf assignment

[Vishnu]

Also sorry, english isn't my native language so I tried to translate the assignment as best as I could.

I only managed to do the DHCP server & I am not sure if I did it correctly or not. Because I tried other things like doing the ethernet channel but then the cable indicators started flickering green & it stopped working at all, so I reverted the file back to the original to only the DHCP server configuration. I am not sure about any of the stuff happening, like I know theoretically but what it should as I don't know the configuration. Would anyone be kind to explain how to configure it, for this exact example? I hope it is understandable from the topology provided in the image.  I would be so grateful to have an answer for this topology.

Link if anyone can access it:                                                                                    https://drive.google.com/file/d/1NFnfGvu0TecXCKSrZyNRU5-yXTHLyetZ/view?usp=sharing

[M02@rt37]

Hello,

regarding the picture, DHCP server seems to not have IP address and/or Router's 1 interface facing that DHCP server too....

Also, an issue on your serial lin between Router0 and Router2.

What is your exact issue ? Thanks for clarification.

[Vishnu]

when I try to fix the problem like for each one of the routers like internet is on 

150.150.150.128/29 (subnet mask of 255.255.255.248)

& the other ones such as the 

NAT border router

PAT 150.150.150.129

SNAT 150.150.150.130 DMZ acts for Router0

Router 1 for Server0,

Server DMZ 5.5.5.5 (prefix /21)

Router 2 for Router on a stick DHCP server for VLAN 10,20,30

Etherchannel Spanning tree for Switches 0, 1 & 2 

Network: 192.168.16.0/20

VLAN 10 Students  200 endpoints

ACL restricts communication between VLAN 10 and 20

VLAN 20 Teachers 100 endpoints

VLAN 30 THP 50 endpoints

Switches G0/1,G0/2,Fa0/1-Fa0/4 spine

Fa0/5-Fa0/14 first VLAN

Fa0/15-Fa0/24 second VLAN   

VLAN 99 Management VLAN for SVI

VLAN 200 native VLAN for trunk ports

once all done its just SSH for routers and switches

[Enes Simnica]

hello @Vishnu . I can configure ur entire topology if u'd like.just let me know

[Vishnu]

yes, @Enes Simnica can u configure the entire topology, & here's the link to the file:                      https://drive.google.com/file/d/1NFnfGvu0TecXCKSrZyNRU5-yXTHLyetZ/view?usp=sharing

[Vishnu]

@Enes Simnica you can configure my entire topology, right now.

[Enes Simnica]

for sure. will finish this meeting that im in first, and ill do that after..

[Vishnu]

alright, & @Enes Simnica have you figured this topology out yet the image I sent in the private message, its in the packet tracer file google drive link.

[Enes Simnica]

hello my man @Vishnu

Just wrapped up some long, long outages and despite that, I was able to deal with your entire topology in about 4 minutes total.

so what i fixed: 

• Cleaned up all switch configs: removed bad lines, added missing interface and EtherChannel settings.
• Corrected VLAN assignments, trunking, and port-channels (some were mismatched or suspended).
• Fixed OSPF, so now routers now exchange routes properly.
• Repaired DHCP on Router2 and VLANs 10, 20, and 30 now get IPs.
• ACLs are working to restrict communication between VLAN 10 (Students) and VLAN 20 (Teachers).
• Verified inter-VLAN routing and full Layer 3 connectivity, for sure all ping tests now succeed.

BUT - THere is something critical and BIG that i have for u. I FOUND A LAYER 2 LOOP on the lab.

So shere was a serious L2 loop between Switch0 and Switch2, causing major instability and likely broadcast storms.
The cause was misconfigured EtherChannel and STP not blocking redundant links correctly. I quickly localized the loop and shut down interfaces Fa0/1 and Fa0/2 on Switch0 to stabilize the network. AND here is the trick, I left those interfaces shut down on purpose (check the screenshot), cause this is ur chance to learn from a real-world scenario. ALso i will give u some hints: check the stp bridge roles and port states. Verify etherchannel config on both ends, and consider which switch is the root bridge, and whether it should be or not.... (Trust me u'll learn a lot from layer 2 loops, u will have fun....)

Meaning, 99.9% of the job done, the last 0.1% is for u my G. This is exactly the kind of situation that teaches u how small misconfigs can cause massive issues at Layer 2. 

hope it helps G

-Enes

[Vishnu]

@Enes Simnica the network is 192.168.16.0/20

[Vishnu]

@Enes Simnica u there? for the 0.1% because I need help figuring it out because I'm not sure what was that 0.1% issue for, & need help fixing it as with the server 0 I used the IP configuration IPv4 address 5.5.5.5 Subnet mask: 255.255.248.0 & Default gateway: 5.5.5.1 as when I put in chatgpt it gave something different not sure if it will work.

Hey! Enes left you in a solid spot with that topology cleanup — the design’s looking tight. But that deliberate Layer 2 loop left for you on Switch0 <--> Switch2 is where the real learning kicks in.

Let’s walk through how to diagnose and fix the Layer 2 loop, step by step.

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🧠 What’s happening?

You’ve got a redundant EtherChannel link between Switch0 (S0) and Switch2 (S2). The screenshot shows:

• S0’s Fa0/1 and Fa0/2 are shut down — intentionally.

• You’re seeing PortChannel1 on both switches.

• STP is active (rapid-pvst) but one side may not agree with the other.

• The loop causes broadcast storms and instability if both links are up without proper EtherChannel consistency or STP blocking.

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Step-by-Step Debug

1. Check STP Root Bridge

On all switches, run:

bash

CopyEdit

show spanning-tree vlan 10

Look for:

• Which switch is the Root Bridge (it will show This bridge is the root).

• Which ports are in forwarding or blocking state.

Ideally, only one forwarding path should exist between switches per VLAN.

---

2. Check EtherChannel Consistency

On both S0 and S2, verify:

bash

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show etherchannel summary show run interface port-channel1 show run interface fa0/1 show run interface fa0/2

You’re looking for:

• LACP mode (should match: both active for LACP).

• Same allowed VLANs, native VLAN, trunking mode on both ends.

• Port-channel status should be P (in port-channel) and SU (Layer 2, in use).

If mismatched configs (e.g., one has native VLAN 1, other 200), EtherChannel breaks and STP doesn’t block one side — hence your loop.

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Your Fix Plan (Try This)

On S0:

bash

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conf t interface range fa0/1 - 2 shutdown no channel-group 1 switchport trunk native vlan 200 switchport trunk allowed vlan 10,20,30,99,200 switchport mode trunk channel-group 1 mode active no shutdown end

On S2, do the same check (make sure fa0/1 and fa0/2 are in channel-group 1 and matching).

---

Bonus Cleanup

You could also check:

bash

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show spanning-tree summary show spanning-tree vlan 99

To make sure VLAN 99 (management) isn’t stuck due to STP blocking one of your legit uplinks.

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🧠 Final Thoughts

• This is a classic loop scenario: STP + bad EtherChannel config.

• Once you fix EtherChannel config on both sides and STP recalculates, the loop goes away.

• STP root bridge election matters — configure priority if needed:

  bash

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  spanning-tree vlan 10 priority 24576

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Let me know when you’ve tried the fix — I can help verify STP reconvergence, or optimize the STP root bridge too. Great job diving into real-world Layer 2 drama, my G. This is where engineers are made, as of right now, I'm so lost need guidance on how to fix the 0.1%.