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Introduction:
Microsoft has released a public preview of a significant update to Azure Private Link Service, removing the mandatory dependency on a Standard Load Balancer. This new capability, known as Private Link Service Direct Connect, allows organizations to expose services via Azure’s private backbone to any routable IP address, whether inside Azure, on-premises, or even in other cloud providers like AWS. For cybersecurity architects and network engineers, this feature fundamentally alters hybrid connectivity strategies, enabling “IP-based service publishing” without complex routing or VNet peering, but it also introduces critical security considerations regarding traffic visibility and firewall inspection.
Learning Objectives:
- Understand the architectural shift from Load Balancer-dependent Private Link Services to direct IP targeting.
- Learn how to configure Private Link Service Direct Connect for scenarios involving overlapping IP spaces and multi-cloud connectivity.
- Identify the security blind spots created when traffic bypasses traditional inspection points like Azure Firewall.
- Implement network monitoring and logging strategies to maintain visibility over PLSDC traffic.
You Should Know:
- Rethinking Private Link: From PaaS Endpoint to Universal On-Ramp
Traditionally, Azure Private Link was primarily associated with Private Endpoints—injecting PaaS services (like SQL or Storage) into a VNet to keep traffic off the public internet. The lesser-known counterpart, Private Link Service (PLS), allowed service providers to expose their own applications behind a Standard Load Balancer to consumers via Private Endpoints. The limitation was the rigid requirement of the Load Balancer.
With the new Direct Connect feature, the Standard Load Balancer is no longer mandatory. You can now point a Private Link Service directly to any routable IP address within your reachable network. This means you can publish a legacy database running on a static IP, a virtual appliance, or even an EC2 instance in AWS, as a first-class Azure Private Link Service.
- Step-by-Step: Configuring PLS Direct Connect for an On-Premises Database
To illustrate, imagine a legacy on-premises database (IP: 10.200.1.10) that cannot be moved or placed behind a load balancer. You want to grant secure access to an Azure VNet without setting up a VPN gateway or exposing the database to the internet.
Prerequisites:
- Azure subscription with access to the Public Preview (registration may be required).
- Network connectivity between Azure and the target IP (e.g., ExpressRoute or VPN).
- The target IP must be routable from the Azure VNet where the PLS is deployed.
Configuration Steps (Azure CLI):
1. Create a Private Link Service Resource:
Unlike the previous method, you will not associate a Load Balancer. Instead, you define the frontend IP configuration using the target IP.
Create a Private Link Service with direct IP configuration az network private-link-service create \ --resource-group MyResourceGroup \ --name MyDirectPLS \ --vnet-name MyHubVNet \ --subnet MySubnet \ --private-ip-address 10.0.0.100 \ --private-ip-version IPv4 \ --destination-ip-address 10.200.1.10
2. Approve the Private Endpoint Connection:
Consumers in other VNets will create a Private Endpoint targeting this service. As the service owner, you must approve the connection.
List pending connections az network private-link-service show --name MyDirectPLS -g MyResourceGroup --query privateEndpointConnections Approve a specific connection (using the Connection ID from the query) az network private-link-service connection update \ -g MyResourceGroup \ -n PendingConnectionName \ --service-name MyDirectPLS \ --connection-status Approved
- Mitigating the “Blind Spot”: Traffic Inspection and Routing
A critical security observation raised by community expert Mo . ✔️☁️ is that Private Link traffic uses the Azure backbone and bypasses forced tunneling and Azure Firewall by default. If your security policy requires logging all traffic or performing intrusion detection, PLSDC traffic will become invisible.
Solution: Route Injection and UDRs
To force PLSDC traffic back through a firewall, you must manipulate the effective routes on the consumer VNet where the Private Endpoint NIC resides.
- Identify the Service IP Range: The target IP range (e.g., the on-premises subnet 10.200.0.0/16) is the destination.
- Create a Route Table: Associate it with the subnet containing the Private Endpoint.
- Add a Route: Set the destination prefix to the target range (e.g., 10.200.0.0/16) and the Next Hop Type to “Virtual Appliance,” specifying the IP of your firewall (e.g., 10.0.1.4).
This forces the traffic from the VM, destined for the database via the Private Endpoint, to first traverse the firewall before hitting the Azure backbone.
- Multi-Cloud and Overlapping IPs: The Killer Use Case
Salman Kazi highlighted the win for overlapping IP spaces. If your Azure VNet (10.0.0.0/16) and AWS VPC (10.0.0.0/16) overlap, you cannot use standard VPC Peering or VPNs without complex NAT.
With PLSDC, you can bypass this entirely.
- In Azure, create a Private Link Service pointing to the public IP of an AWS NAT Gateway or the private IP of an AWS resource (provided there is a VPN/DC link).
- The consumer in Azure connects to the Private Endpoint for this service.
- Result: Azure routing treats the traffic as a private connection to a service, completely ignoring the overlapping IP conflict because the endpoint exists in the Azure SDN fabric, not as a direct route to the AWS network.
5. Auditing and Logging PLSDC Connections
With the removal of the Load Balancer, diagnostic logging shifts. You must now rely on the Private Link Service logs.
Enable Logging via PowerShell:
Get the resource ID of the Private Link Service $PLS = Get-AzPrivateLinkService -ResourceGroupName "MyResourceGroup" -Name "MyDirectPLS" Enable Diagnostic Setting Set-AzDiagnosticSetting ` -ResourceId $PLS.Id ` -Name "PLSLogs" ` -Enabled $true ` -Category 'PrivateLinkServiceVisibility' ` -Category 'PrivateLinkServiceFlowEvents' ` -WorkspaceId (Get-AzOperationalInsightsWorkspace -ResourceGroupName "LogRG" -Name "MyLogAnalytics").ResourceId
These logs capture metadata about connections (source IP, status, bytes transferred) but not the payload. For payload inspection, the forced tunneling method mentioned in Section 3 is mandatory.
6. Windows/Linux Connectivity Testing
Once the Private Endpoint is deployed, connectivity testing is standard. From a VM in the consumer VNet, you should be able to reach the service by its Private Endpoint IP or FQDN.
- From Linux (using Netcat to test port):
nc -vz 10.0.0.100 3306 Expected output: Connection to 10.0.0.100 port 3306 [tcp/mysql] succeeded!
- From Windows (using Test-NetConnection):
Test-NetConnection -ComputerName 10.0.0.100 -Port 3306 Expected: TcpTestSucceeded : True
What Undercode Say:
- Architectural Liberation: PLSDC removes a significant bottleneck, allowing for cleaner, infrastructure-light hybrid designs. It effectively turns Azure’s backbone into a giant, private software-defined WAN connector.
- Security Trade-off: The convenience comes with a security cost. By default, traffic becomes invisible to centrally managed firewalls. Organizations must proactively implement User-Defined Routes to reinspect traffic, turning a “simple” connection into a potentially complex routing puzzle.
- The death of the “Overlap” Excuse: One of the biggest technical hurdles in M&A and multi-cloud (overlapping IPs) now has a native, elegant solution. This will accelerate hybrid and multi-cloud adoption.
Prediction:
This feature will catalyze a new wave of “Network Segmentation as a Service.” Expect to see a rise in third-party security vendors offering virtual appliances specifically designed to sit as the target of a PLSDC, acting as security proxies for external databases. Furthermore, as adoption grows, Microsoft will likely need to introduce more granular policy controls within the Private Link fabric itself to allow or deny traffic without forcing it through external firewalls, potentially evolving Private Link into a more robust Zero Trust network access point.
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Reported By: Matthansen0 Public – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
