29_1: Overview of Telnet

Telnet is a network protocol used to establish a remote connection to a device or server over TCP. It allows users to test port reachability and troubleshoot network connectivity issues by verifying if a specific port on a target server is open and reachable. However, since Telnet transmits data in plain text and lacks encryption, it is typically used for troubleshooting purposes in controlled environments and is not recommended for production systems.

29_2: Introduction

In this lab, we will use Telnet to verify the port reachability between two compute instances in the same subnet in Oracle Cloud Infrastructure (OCI). The goal is to confirm whether the required port on one instance is open and accessible from the other instance. If the Telnet connection fails, we will identify and resolve the issue. By the end of this lab, you will:

• Understand how to use Telnet to test port reachability between OCI instances.
• Learn how to troubleshoot connectivity issues by modifying security configurations such as VCN Security Rules, NSGs, and firewall settings.
• Successfully verify port reachability in a controlled OCI environment.

29_3: Install Telnet

29_3_A: Open two instances in PuTTY and run below command to know host's IP.

hostname -ip

29_3_B: Attempt to access their ports(22)

telnet (Opposite Instance Host IP) 22

29_3_C: Telnet not found.

29_3_D: Install Telnet

yum install telnet

Type y and Now telnet has been downloaded.

Again we try to connect to another instance via telnet and we are still unable to connect.

29_4: Enable Connectivity

29_4_A: Copy the IP of Subnet (Public/Private)

Navigate to Networking-->Virtual Cloud Networks-->VCN-->Subnets

29_4_B: Check the ingress rules for the TCP protocol

29_4_C: Add ingress rules.

Source: Copied Public Subnet Protocol: TCP Port: 22

29_4_D: Ingress Rule is created.

29_5: Reconfirming Connectivity

Telnet IPS and we can see IPs are connected.