Skip to main content

What if my public address is same as one of the IP address in my AWS VPC CIDR Block? [Resolved]

My public IP address (of my personal computer) from which I access the internet ranges from 112.110.x.x. For experiment, I created a VPC in AWS and chose the CIDR block as 112.110.0.0/16. In the route table, destination IP 112.110.0.0/16 has a target "local". I launched an EC2 instance in this VPC which uses this CIDR block 112.110.0.0/16 for internal IP assignment. Now, I am unable to connect to this instance from my local computer even though NACL allows 0/0 inbound and outbound traffic, and I've even allowed 0/0 traffic in the Security Group of this instance.

I want to know:

  1. Do route tables reserve CIDR block IP address for both inbound as well as outbound connections and blocks all incoming internet (from outside the private network) traffic from any IP address which falls under the reserved IP address range in the CIDR block?

  2. Is there any way for me to connect to this instance from local computer directly without using any VPN or a bastion host?


Question Credit: Sanjay Vig
Question Reference
Asked July 20, 2019
Posted Under: Network
26 views
1 Answers

That 112.110.x.x belongs to Idea Cellular Ltd, you shouldn’t use it in your VPC. Instead choose one of the reserved “private IP ranges” (RFC1918): 10.0.0.0/16, 172.16.0.0/12 or 192.168.0.0/16

Having said that you should still be able to connect to your EC2 instance.

  1. Make sure it’s got a Public IP address assigned, it will probably be something like 3.x.x.x or 52.x.x.x or something like that.

  2. Find out your public IP address, for example through ifconfig.co - lets say it’s 112.110.12.34.

  3. In your VPC route table add a route for your public IP (e.g. 112.110.12.34) via your IGW.

That should work. However I strongly suggest against using non-RFC1918 addresses in your VPC, it’s only calling for problems.

Hope that helps :)


credit: MLu
Answered July 20, 2019
Your Answer
D:\Adnan\Candoerz\CandoProject\vQA