Troubleshoot -Connection issue ( Recreate Security list, Gateway, Route)

Troubleshoot Recreate Security list (Firewall)

Step 1. Go to Networking - Virtual cloud networks -

Step 2. Now Select Hub_Network_Compartment becuase our Virtual Network we create in Network compartment.

Step 3. Now Click on Subnets after this click on Public subnet-HUB_NETWORK becuase our instance connected with the public network.

Step 4. Click on Default Security List for HUB_NETWORK and after this click on security rules

Inside the Default Security List for HUB_NETWORK we found 2 important rules for instance connectivity.

Egress Rule & Ingress Rule

🔹 Ingress Rules (Inbound Traffic)

Purpose: Control traffic coming into your subnet or instance.

Example: Allow SSH (port 22) from your office IP.

Key Fields:

Source: Defines where the traffic originates (CIDR block, IP, or NSG).

Protocol & Port: e.g., TCP, UDP, ICMP, with specific port ranges.

Action: Always "Allow" (OCI doesn’t support explicit deny in security lists).

👉 Ingress rules protect your resources by restricting who can connect to them.

🔹 Egress Rules (Outbound Traffic)

Purpose: Control traffic going out from your subnet or instance.

Example: Allow all outbound traffic to the internet (0.0.0.0/0).

Key Fields:

Destination: Defines where the traffic is allowed to go (CIDR block, IP, or NSG).

Protocol & Port: Same as ingress, you can restrict by protocol/port.

Action: Always "Allow."

👉 Egress rules prevent instances from sending traffic to unwanted destinations.

To connect or login into putty highlighted rules compulsory.

In the highlighted area We can see ""TCP traffic for ports: 22 SSH Remote Login Protocol"" these rules allow us to login into the putty or server.

We login into the server successfully.

Step 5. Now we check when we remove these rules and check what happened next .

Step 6. After remove the rule we show we are not able to login and get an error.

Step 7. In this step we recreate the rule Ingrees rule.

Step 8. After adding the rules we try to login again into the putty and we show that we are now able to login into the putty successfully without any error.

Troubleshooting Route & Gateway

Step 1. Inside public subnet-HUB_NETWORK we will see the route table- default route table for HUB_NETWORK click on this.

This Highlighted Internet Gateway rule able to us connect with the server. if we remove this rule so we can't login into the server.

After removing this rule we try to login into putty, but we can't login and getting a error.

Step 2. Go to HUB_NETWORK and click on Gateway after we terminate the internet gateway and try to login into the putty application.

After removing this internet gateway rule we try to login into putty, but we can't login and getting a error.

Step 3 Now recreate route

We see that here is not gateway found. so we can't create a rout without a gateway so now first we create gateway and after this we create rout.

Step 4. Create Internet Gateway

Step 5. Now we create Route

Step 6. now we again try to login in putty and we see that now we can login successfully into the putty.