Microsoft Entra Private Access is a powerful zero-trust network access solution that is remarkably simple to install and configure. Administrators can quickly install the Global Secure Access (GSA) agent on their endpoints, then install the Entra Private Network Connector to enable secure remote access to private, internal resources. However, the ease with which Entra Private Access can be configured can potentially lead to connectivity issues in some scenarios. This post demonstrates how to diagnose port exhaustion issues and expand the available port range to address them.
Entra Private Network Connector
The Entra Private Network Connector is a key component of the Entra Private Access solution. The Private Network Connector is essentially the old Azure Application Proxy, enhanced to support TCP and UDP applications in addition to HTTP-based web applications. It is installed on an on-premises Windows server to provide GSA clients with access to internal data and applications.
Network Connectivity
The GSA client is not a virtual network adapter like most traditional VPN clients. Instead, the GSA client installed on the client operates as a filter driver in the network stack, selectively intercepting traffic and tunneling it over the GSA tunnel based on configured policy. As such, it does not appear as a network adapter in the operating system and does not have its own IP address.
Translation
When traffic from the GSA client is routed over the Entra Private Network Connector, the traffic egressing from the connector server to the internal network is effectively translated. That is, the source IP address of traffic destined for an internal resource is the connector server’s IP address, not the client’s original source IP address.
Port Exhaustion
The ephemeral port range on Windows servers spans from 49152 to 65535, leaving only 16,384 ports available. This can easily be exhausted when many clients are connected to a single Entra Private Network Connector server. This pool can also be depleted by poorly written or badly behaving applications that needlessly open many socket connections to internal resources.
Troubleshooting
Administrators can view the ephemeral port configuration for both TCP and UDP by running the following commands.
netsh.exe interface ipv4 show dynamicportrange protocol=tcp
netsh.exe interface ipv4 show dynamicportrange protocol=udp
To determine if port exhaustion is an issue, open an elevated PowerShell command window and run the following command.
Get-NetTcpConnection | Where-Object State -match ‘established’ | Measure-Object
Next, run the following PowerShell command to identify the number of ports consumed exclusively by the Entra Private Network Connector.
$ProcessId = Get-CimInstance -ClassName win32_service | Where-Object Name -eq ‘WAPCSvc’ | Select-Object -ExpandProperty ProcessID
Get-NetTCPConnection | Where-Object { $_.State -match ‘established’ -and $_.OwningProcess -eq $ProcessId } | Measure-Object
If the number of ports consumed by the Entra Private Network Connector approaches the upper limit of available ports, administrators should increase the ephemeral port range to ensure the connector server operates reliably.
Note: Use the Get-NetUdpEndpoint PowerShell command to monitor UDP port consumption on Entra Private Network Connector servers.
Resolution
To increase the ephemeral port range on the Entra Private Network Connector server, open an elevated command window and run the following commands.
netsh.exe interface ipv4 set dynamicportrange protocol=tcp startport=10000 numberofports=55535
netsh.exe interface ipv4 set dynamicportrange protocol=udp startport=10000 numberofports=55535
netsh.exe interface ipv6 set dynamicportrange protocol=tcp startport=10000 numberofports=55535
netsh.exe interface ipv6 set dynamicportrange protocol=udp startport=10000 numberofports=55535
Running these commands will increase the number of available ephemeral ports on the server to more than 50,000, well above the default. In most cases, this should be sufficient to handle many GSA client connections. However, administrators are cautioned to monitor port usage on the Entra Private Network Connector servers to ensure continued reliable operation. It may be necessary to deploy additional connector servers to process the existing workload.
Summary
Entra Private Network Connectors can exhaust the default 16,384-port ephemeral range when many GSA clients access internal TCP/UDP resources. Administrators can diagnose the issue by filtering Get-NetTCPConnection results by the WAPCSvc process, then expanding the range to over 50,000 ports using netsh.exe, as shown above. Monitor usage continuously in high-load environments to ensure consistent and stable access. And if you find you need more than 50,000 ports per server, it’s probably time to deploy additional connector servers. 😊
Additional Information
Microsoft Entra Private Access
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