Question 

I want to know which resource is using a specific IP address assigned in a subnet. 

Resolution 

You can identify the resource by following the steps below. [1] 

1. Open the Amazon Elastic Compute Cloud (Amazon EC2) console. 

2. In the navigation pane, choose Network Interfaces. 

3. Click the search box and select Primary private IPv4 address.
   If you are looking for a public IP, click the search box and select Public IPv4 address instead. 

4. Enter the IP address you are investigating in the search box.
   A list of network interfaces that match the search criteria appears.
   (Alternatively, you can enter the IP address directly in the search box without setting any filters.) 

5. In the lower panel, read the Description of the network interface and identify the resource that owns the interface. Alternatively, you can use the AWS CLI to find the network interface that owns the IP address: 

   aws ec2 describe-network-interfaces --filters Name=addresses.private-ip-address,Values=IPv4 address

Notes 

• Replace IPv4 address with the IP address you are investigating. 

• Make sure that the correct region is configured. If not, specify the region manually using the --region parameter. 

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[1] How do I find the resource that's using an unknown IP address in my Amazon VPC?
https://aws.amazon.com/ko/premiumsupport/knowledge-center/vpc-find-owner-unknown-ip-addresses/