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New Member

Duplicate IP

Hello friends, I wrote these lines because a very strange and particular issue happened in my network.


There is a drawing of my topology: 

I will explain first:


1. I have a big network ( so I'm planning to cut it in VLANs. Since the network is 24/7 alive, I can't cut the service at once, so I decide to have 2 links: one in Layer 3 and another one in Layer 2. It works perfectly


2. I'm using the switch Core as ISP, so there is a default route from Distribution to Core


3. As I can't configure the access switch (port labeled as switchport), I let the ports in L2. The green line means that the port in distribution switch is in L3 and port in access switch is in L2


The issue: All the PCs in my network got the message of Duplicate IP, guess with which ip we had the issue? Well, it was with the L3 interface in distribution switch


My question is, what this could happen?! PCs are in network and the L3 link is network, at my sight, it is impossible


What do you think?


Thanks in advance for your answers!

Everyone's tags (1)
New Member

What is the IP address of

What is the IP address of DHCP server ? Can you do a show ip with all association IP address - MAC address ?

New Member

Walter, I wasn't using a DHCP

Walter, I wasn't using a DHCP server, everything was configured with static IP.

New Member

What is the message ? IP 172

What is the message ? IP 172.16.x.x duplicate ip with 10.0.0.x ?

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