Step by step procedure to troubleshoot the Point to point connectivity

Scenario where client want is unable to send anything from his Instace.

In that case will check below mentioned steps one by one and troubleshoot if any issue exits.

1. Will check is there any planned outage from Oracle side or not if yes will ask client to wait for sometime.
2. Will check RT
3. Will check SL
4. Will check Firewall

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What is a Route Table?

A Route Table is a set of rules (routes) that determine where network traffic should be directed based on the destination IP address.

Key Characteristics

• Operates at: Subnet level
• Based on: Destination IP CIDR and priority
• Routes to: Internet Gateway, NAT Gateway, VPN, DRG, etc.
• Longest prefix match: Most specific route is used
• Default route: 0.0.0.0/0 (catch-all)

What is a Security List? A Security List is a stateful firewall at the subnet/instance level that controls inbound (INGRESS) and outbound (EGRESS) traffic using rules.

Key Characteristics

• Stateful: If you allow outbound traffic, response inbound traffic is automatically allowed
• Operates at: Subnet or instance level
• Rules based on: Protocol, port, source/destination IP/CIDR
• Default behavior: Deny all (unless rule allows)

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What is a Firewall? A host-level firewall is software-based traffic control running on the instance OS (separate from Security Lists). It provides an additional layer of security beyond Security Lists.

Key Characteristics

• Operates at: Operating System/Host level
• Tools: iptables (Linux), Windows Firewall (Windows)
• Operates after: Security Lists and Route Tables
• Can be: More granular than Security Lists
• Performance: Slightly higher latency than Security List

Step-by-Step Firewall Configuration (Linux)

# Check if firewall is running

sudo systemctl status firewalld

OR

sudo systemctl status ufw

# Check iptables rules

sudo iptables -L -n

# Check ufw status

sudo ufw status

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