Why do we have to add Internet Gateway into the Route Tables to receive the internet traffic

Question

Route tables describe the destination of packets from within a VPC, so why does a route table have to include an internet gateway when the internet gateway is itself a source of the packet and the destination is the public or elastic IPs within the VPC?

Answer 1

Because almost every useful internet connection is bidirectional. TCP/IP connections require several packets back and forth before a connection is established and even if, abstractly, all of the data is going one way, there's a flow of acknowledgement packets returning to the sender. This isn't the case with UDP/IP, but I don't know exactly what traffic you're trying to send back-end forth. One thing you could try is to install tcpdump (or similar) on the instance and see if it receives the packets. (It is possible to do this without the AWS IGW, however, it will require a second VPC, VPC peering, and a bit of clever network configuration.)

Answer 2

Hi,

Please find the below explanation, kindly correct me if I am wrong:

Here route tables are used to route the table is a set of rules used to determine the network in which it has to be directed.

Each VPC has its own routing table to send/receive traffic.

Where internet gateway is used to connect the internal IP addresses to the internet or vice-versa.

Summary:

In general, routing table routes the traffic internally in the AWS network but for the IGW it is to contact the outside network basically internet.