Technical Tip: Azure traffic flow limitation

When the number of network connections on an Azure virtual machine approaches or exceeds its flow limits, connection drops and degraded performance can result.

Flow Limits Overview.

Azure VMs support up to 500,000 active flows in each direction (inbound and outbound), and 1 million total flows per VM for standard scenarios. Network virtual appliances (NVAs) like firewalls and proxies are limited to 250,000 active connections, as traffic is forwarded and more flows are created per connection.

Exceeding the flow limit will lead to:

• Dropped Connections: When the active connection limit is reached, new connection attempts will be dropped, causing application connectivity issues and potential service outages.
• Performance Degradation: Connection establishment and termination share CPU resources with packet processing, so high connection rates can reduce overall network and VM performance.
• Network Bottlenecks: Reaching the flow limit prevents scaling beyond the predefined connection count, so workloads with higher connection needs require scaling out to additional VMs.
• Difference in Metrics: The number of flows tracked by the guest OS within the VM may differ from the number tracked by the Azure network stack.

Summary Table:

Related document: 

Virtual machine network bandwidth