In this article, we will analyze the causes of intermittent VM networking failures in Azure, explore debugging techniques, and provide best practices to ensure stable and reliable network connectivity.

Understanding Azure VM Networking Failures

Intermittent networking failures occur when Azure VMs lose connectivity without consistent patterns. Common causes include:

  • Fluctuations in Azure virtual network (VNet) performance.
  • Conflicts in network security group (NSG) rules.
  • Azure Load Balancer session persistence issues.
  • DNS resolution failures in Azure private networks.
  • Unexpected changes in virtual network peering.

Common Symptoms

  • Azure VMs randomly losing connection to the internet or internal resources.
  • Sudden SSH/RDP session disconnections.
  • Services failing due to unreachable backend VMs.
  • DNS resolution errors when resolving private endpoints.

Diagnosing Azure VM Networking Issues

1. Checking Azure VM Network Configuration

Verify the current network settings for a VM:

az network nic show --resource-group myResourceGroup --name myNIC

2. Analyzing Network Security Groups (NSGs)

List active NSG rules and check for unintended blocks:

az network nsg rule list --resource-group myResourceGroup --nsg-name myNSG

3. Verifying Azure Load Balancer Health Probes

Check if the backend VM is responding correctly:

az network lb probe show --resource-group myResourceGroup --lb-name myLoadBalancer --name myHealthProbe

4. Diagnosing DNS Resolution Failures

Verify DNS resolution inside an Azure VM:

nslookup myprivateendpoint.database.windows.net

5. Checking Virtual Network Peering

Ensure peering configurations are correctly set:

az network vnet peering list --resource-group myResourceGroup --vnet-name myVNet

Fixing Azure VM Networking Failures

Solution 1: Adjusting Network Security Group Rules

Allow necessary inbound and outbound traffic:

az network nsg rule create --resource-group myResourceGroup --nsg-name myNSG --name AllowSSH --priority 100 --direction Inbound --access Allow --protocol Tcp --source-port-range "*" --destination-port-range 22

Solution 2: Enabling Accelerated Networking

Improve network performance with accelerated networking:

az network nic update --name myNIC --resource-group myResourceGroup --accelerated-networking true

Solution 3: Fixing Azure Load Balancer Configuration

Ensure session persistence is enabled for consistent routing:

az network lb rule update --resource-group myResourceGroup --lb-name myLoadBalancer --name myRule --protocol Tcp --frontend-port 80 --backend-port 80 --load-distribution SourceIP

Solution 4: Configuring Custom DNS for Private Endpoints

Ensure correct DNS resolution for internal services:

az network private-dns record-set a add-record --resource-group myResourceGroup --zone-name myprivatezone.com --record-set-name myservice --ipv4-address 10.0.0.4

Solution 5: Validating and Recreating Virtual Network Peering

Recreate broken VNet peering connections:

az network vnet peering create --name myPeering --resource-group myResourceGroup --vnet-name myVNet --remote-vnet myRemoteVNet

Best Practices for Azure VM Networking Stability

  • Regularly review and audit NSG rules to prevent accidental blocks.
  • Enable Azure accelerated networking to reduce packet loss.
  • Configure proper health probes for Azure Load Balancer.
  • Use private DNS zones for reliable service discovery.
  • Monitor network logs to detect anomalies early.

Conclusion

Intermittent Azure VM networking failures can cause disruptions in cloud environments. By managing NSG rules, enabling accelerated networking, configuring DNS correctly, and monitoring network performance, organizations can ensure reliable and stable Azure deployments.

FAQ

1. Why do my Azure VMs randomly lose connectivity?

Network security group rules, virtual network peering issues, or DNS misconfigurations may be causing connectivity drops.

2. How can I diagnose Azure networking issues?

Use Azure CLI commands like az network nsg rule list and az network nic show to inspect network configurations.

3. Can I improve Azure VM network performance?

Yes, enabling accelerated networking can improve packet processing efficiency and reduce latency.

4. Why are my private endpoints not resolving?

Check if private DNS records are correctly configured for your internal services.

5. How do I fix issues with Azure Load Balancer?

Ensure health probes are correctly configured and enable session persistence for consistent routing.