Issues with NAT Gateway and Public IP Configuration - No Internet Access

Question

Hello,

I am experiencing an issue where my virtual machine (VM) loses internet access when the NAT Gateway is configured. Below are the details of the problem:

---

Current Configuration:

VM Configuration:

The VM is using a private IP address only.

  Public IP has been **removed** from the VM.
  
  **NAT Gateway Configuration**:
  
     A **NAT Gateway** has been configured on the **subnet** of the VM.
     
        The subnet is correctly attached to the NAT Gateway.
        
        **Testing**:
        
           **When only the Public IP is attached to the VM**, the internet works without issues.
           
              **When the NAT Gateway is configured**, internet access stops working completely (no internet).
              
                 **When the Public IP is configured along with the NAT Gateway**, internet access is still not working.
                 

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Troubleshooting Steps Taken:

Verified that the NAT Gateway is configured and attached to the correct subnet.

Ensured there are no conflicting route tables or network security group (NSG) rules.

Checked that the subnet is properly linked to the NAT Gateway.

---

Expected Behavior:

When the NAT Gateway is configured, all outbound traffic from the VM should route through the NAT Gateway, allowing internet access, even without the VM having a Public IP.

---

Request:

Kindly assist in identifying the cause of this issue and provide guidance on how to ensure the internet works correctly when the NAT Gateway is in place.

• Specifically, I suspect there may be a misconfiguration related to the Public IP or NAT Gateway’s routing.Hello Azure Support Team, I am experiencing an issue where my virtual machine (VM) loses internet access when the NAT Gateway is configured. Below are the details of the problem: Current Configuration:
  1. VM Configuration:
     • The VM is using a private IP address only.
     • Public IP has been removed from the VM.
  2. NAT Gateway Configuration:
     • A NAT Gateway has been configured on the subnet of the VM.
     • The subnet is correctly attached to the NAT Gateway.
  3. Testing:
     • When only the Public IP is attached to the VM, the internet works without issues.
     • When the NAT Gateway is configured, internet access stops working completely (no internet).
     • When the Public IP is configured along with the NAT Gateway, internet access is still not working.
  Troubleshooting Steps Taken:
  1. Verified that the NAT Gateway is configured and attached to the correct subnet.
  2. Ensured there are no conflicting route tables or network security group (NSG) rules.
  3. Checked that the subnet is properly linked to the NAT Gateway.
  Expected Behavior:
  • When the NAT Gateway is configured, all outbound traffic from the VM should route through the NAT Gateway, allowing internet access, even without the VM having a Public IP.
  Request:
  • Kindly assist in identifying the cause of this issue and provide guidance on how to ensure the internet works correctly when the NAT Gateway is in place.
  • Specifically, I suspect there may be a misconfiguration related to the Public IP or NAT Gateway’s routing.

Answer 1

Hello,

Welcome to Microsoft Q&A,

NAT Gateway requires the subnet's outbound traffic to be routed correctly. The most common reasons NAT Gateway doesn't allow outbound internet access are:

1. Missing Route Table Update
2. Conflicting User-Defined Routes (UDRs)
3. NSG blocking outbound traffic
4. NAT Gateway not bound properly

#1 - You must not override the default system route 0.0.0.0/0 -> Internet.

• Check if you accidentally attached a Route Table with custom UDRs.
• Go to VM in Azure portal --> Network Settings --> Select the Subnet, and see if the Route table is none or if you have a custom table, add 0.0.0.0/0 for the internet to work.

#4 - NAT Gateway should be attached at the Subnet Level (not VM NIC level).

Azure NAT Gateway architecture expects: (VM Private IP → Subnet → NAT Gateway → Public Internet)

#3 - NSG (Network Security Group) Outbound Rules, Make sure NSG is allowing outbound traffic.

Check:

• Go to NSG attached to your subnet or VM NIC
• Under Outbound security rules:
  • Allow Internet destination
  • Allow Any destination

Please upvote and accept the answer if it helps!!