Floating IP on Azure ILB for SQL Always On Listener

AZ-104 By islever Editorial Last updated

Configure name resolution and load balancing Configure and manage virtual networks in Azure

Short answer

A Enabling Floating IP (direct server return) on the internal load balancer is required so the SQL Always On listener reaches the replica that owns the listener IP.

Question

Note: The question is included in a number of questions that depicts the identical set-up. However, every question has a distinctive result. Establish if
the solution satisfies the requirements.
Your company has a Microsoft SQL Server Always On availability group configured on their Azure virtual machines (VMs).
You need to configure an Azure internal load balancer as a listener for the availability group.
Solution: You enable Floating IP.
Does the solution meet the goal?
  1. Yes Correct Answer
  2. No

Key Takeaways

The question tests whether you know the mandatory load balancing rule settings for a SQL Always On availability group listener — the trap is assuming that enabling Floating IP is optional or merely an outbound-traffic tweak rather than a required listener configuration.

This AZ-104 scenario asks whether enabling Floating IP (direct server return) on an Azure internal load balancer satisfies the requirement of acting as a listener for a SQL Server Always On availability group on Azure VMs. The answer established here is Yes, because direct server return is a required setting on the load balancing rule for the AG listener to function.

Common mistake: The most common wrong answer is B (No), chosen by learners who believe that enabling Floating IP is not part of the listener setup or that additional steps such as the health probe and load balancing rule make the solution incomplete. Floating IP (direct server return) is in fact one of the specific settings Microsoft documents as required on the listener's load balancing rule.

Expert Analysis

Why the Answer Is Correct

Microsoft's guidance for configuring an Azure internal load balancer as a listener for a SQL Server Always On availability group specifies a load balancing rule (typically frontend and backend port 1433) with Floating IP (direct server return) set to Enabled. With direct server return, the load balancer delivers packets to the backend SQL VM without rewriting the destination address, so the request reaches the replica that currently owns the AG listener IP address, and replies go straight back to the client from that listener IP. Because only one replica owns the listener resource at a time, this pass-through behavior is what makes the listener reachable, so enabling Floating IP directly satisfies the stated requirement and the answer is Yes (A). The community's most-supported comment likewise frames the rule configuration as the mechanism that routes traffic to the SQL instances and points to direct server return for the owning instance.

Why the Other Options Are Wrong

Option B (No) would only be justified if Floating IP were irrelevant or harmful to the listener, but it is the opposite: without it, Azure performs destination NAT to the backend VM's own IP, so traffic for the listener IP never reaches the owning replica and client connections fail after failover. Learvers selecting B often argue that a health probe (for example a TCP probe on a high port such as 59999) and the load balancing rule are also needed, which is true of the full end-to-end setup, but those are separate components of the overall solution rather than reasons this particular action fails to meet the goal. The setting being tested here is precisely the one that distinguishes a working AG listener rule from a generic internal load balancing rule, so treating it as insufficient misses the point of the question. Nothing about enabling Floating IP breaks persistence or port reuse for clustering scenarios; it is the recommended configuration for high-availability clustering on the backend pool.

Community Comment Notes

Bloodwar, whose comment carries by far the highest approval, quotes the configuration guidance that the rules "configure how the load balancer routes traffic to the SQL Server instances" and that you "enable direct server return" because only one SQL instance owns the listener at a time — matching the Yes verdict. Ruhi9903 similarly explains that "Floating IP (also called Direct Server Return) ensures the load balancer forwards traffic to the VM without rewriting the destination IP," which is critical for the listener. edengoforit and Timock add the underlying mechanics: with Floating IP enabled, "Azure changes the IP address mapping to the Frontend IP address of the Load Balancer frontend," enabling port reuse across rules. JWS80 dissents with No, arguing Floating IP is not a required step, but that contradicts the documented listener rule configuration; juniorccs's remark that the linked labs are lengthy simply reflects study time, not the correctness of the setting.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

For these 'Does the solution meet the goal?' items, evaluate only whether the single action stated addresses the requirement being tested, not whether a complete real-world deployment would include more steps. For SQL Always On listeners on Azure, remember the rule checklist: internal load balancer, backend pool of the SQL VMs, a health probe, and a load balancing rule with Floating IP (direct server return) enabled.

Frequently Asked Questions

Why does a SQL Server Always On listener on Azure require Floating IP (direct server return)?

Only the replica that owns the listener IP should receive the client's connection. Direct server return delivers packets to that VM without rewriting the destination address, so the reply is sourced from the listener IP.

Is enabling Floating IP alone enough to configure an Azure ILB listener for an availability group?

For this exam question, yes, it is the setting that meets the stated goal. In a full deployment you also need an internal load balancer, a backend pool containing the SQL VMs, and a TCP health probe on the replicas.

More AZ-104 FAQ →

Discussion 50 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 30 of 50

  1. Bloodwar 👍 84
    The load balancing rules configure how the load balancer routes traffic to the SQL Server instances. For this load balancer, you enable direct server return because only one of the two SQL Server instances owns the availability group listener resource at a time. >> Floating IP (direct server return) Enabled
  2. ricardona 👍 37
    Yes, enabling Floating IP on the Azure internal load balancer as a listener for the availability group can meet the goal. By enabling Floating IP, the load balancer will use a floating IP address as the source IP address for outbound flows from the backend pool. This will ensure that the IP address used by the backend pool remains the same even if a VM is restarted or replaced, which is important for maintaining the listener for the availability group.
  3. edengoforit 👍 15
    If you want to reuse the backend port across multiple rules, you must enable Floating IP in the rule definition. When Floating IP is enabled, Azure changes the IP address mapping to the Frontend IP address of the Load Balancer frontend instead of backend instance's IP. Without Floating IP, Azure exposes the VM instances' IP. Enabling Floating IP changes the IP address mapping to the Frontend IP of the load Balancer to allow for additional flexibility. https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-floating-ip
  4. Timock 👍 8
    This is the why: Some application scenarios prefer or require the same port to be used by multiple application instances on a single VM in the backend pool. Common examples of port reuse include: clustering for high availability/network virtual appliances/exposing multiple TLS endpoints without re-encryption. If you want to reuse the backend port across multiple rules, you must enable Floating IP in the rule definition. https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-floating-ip The is the how: The link below is a step by step guide for creating an Azure internal load blancer as a listener for an availability group... "Backend Port 1433. This value is ignored because this rule uses Floating IP (direct server return)." https://docs.microsoft.com/en-us/azure/azure-sql/virtual-machines/windows/availability-group-load-balancer-portal-configure
  5. kamalpur 👍 7
    The floating IP concept is explained in below video
Show 25 more comments
  1. JWS80 👍 5 Answered B
    No, the solution does not meet the goal. Enabling Floating IP is not a required step when configuring an Azure internal load balancer as a listener for a SQL Server Always On availability group. There are several steps involved in configuring an Azure internal load balancer for a SQL Server Always On availability group, including creating the load balancer, configuring the backend pool, creating a probe, and setting the load balancing rules. Enabling Floating IP is not one of these steps.
  2. Ruhi9903 👍 4 Answered A
    SQL Always On listener uses the same IP address for failover between replicas. The ILB must allow the backend pool members (SQL VMs) to respond to traffic without changing their own IP configuration. Floating IP (also called Direct Server Return) ensures the load balancer forwards traffic to the VM without rewriting the destination IP, which is critical for the listener to work correctly.
  3. Madbo 👍 4
    A. Yes, enabling Floating IP on the Azure internal load balancer will allow the Always On availability group to use the IP address assigned to the load balancer even if the virtual machine instance changes. This will ensure that clients can connect to the availability group without interruption in case of a failover.
  4. juniorccs 👍 4
    I went to the links trying to understand it better, but gosh! only the exercise takes hours to be completed, I may try it later, but for the exam, the knowledge in the links share is just too much! Thanks for the short explanation
  5. GabeCanada 👍 4
    Not sure how a floating IP helps with this. From the series it should be something like a TCP 1433 health probe...
  6. ralphmas 👍 3
    The solution provided, enabling Floating IP, does not meet the goal of configuring an Azure internal load balancer as a listener for the availability group. Enabling Floating IP is not the correct configuration option for an Azure internal load balancer listener for SQL Server Always On availability groups. Floating IP is only used for outbound traffic from the virtual machine, and not for inbound traffic from the Azure internal load balancer. To configure an Azure internal load balancer as a listener for the availability group, you need to create an internal load balancer and configure the listener for the availability group. You will then add the IP address of the internal load balancer as the listener IP address for the availability group. Therefore, the correct answer is B. No.
  7. Quantigo 👍 3
    Correct Answer A – Yes Float IP Enabled Reference: https://docs.microsoft.com/en-us/azure/virtual-machines/windows/sql/virtual-machines-windows-portal-sql-alwayson-int-listener
  8. Neowarp 👍 3
    In the articule it's "... 1433. This value is ignored because this rule uses Floating IP (direct server return). ..." in Step 4: Set the load-balancing rules ...
  9. harendradhiman 👍 3 Answered A
    Azure Load Balancer Floating IP configuration explanation: https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-floating-ip
  10. tsummey 👍 2 Answered A
    In the context of SQL Server Always On AG, the Floating IP is crucial because it provides a consistent endpoint for the AG listener. To support failover Handling, Azure VNets do not support broadcasting, so the Floating IP and the internal load balancer’s probe setup help determine which node is the primary replica and direct application traffic to it without the need for broadcasting.
  11. liza1234 👍 2
    No. If you enable floating IP, the ILB listener will not be able to tell whether a single mssqlserver is down because the ip addresses of all the VMs are the same. Your ILB won't have a mechanism to distinguish the down VM's because they lose their individual identity/IP by enabling the floating IP. The best solution is to create HTTP Health Probe on Port 1433.
  12. Mev4953 👍 2
    https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-floating-ip#:~:text=If%20you%20want%20to%20reuse%20the%20backend%20port%20across%20multiple%20rules%2C%20you%20must%20enable%20Floating%20IP%20in%20the%20rule%20definition.
  13. GabeCanada 👍 2
    Enabling floating IP is listed in the KB but that alone does provide a full solution for it as this is just a config in a rule. But in this series that's the correct answer.
  14. JohnPhan 👍 2
    Yes Floating IP (direct server return) Enabled https://docs.microsoft.com/en-us/azure/azure-sql/virtual-machines/windows/availability-group-load-balancer-portal-configure
  15. Naru60 👍 2 Answered A
    If Floating IP is not enabled, the connection destination will not switch correctly when connecting via a listener in the Availability group.
  16. Surinam 👍 2
    At a platform level, Azure Load Balancer always operates in a DSR flow topology regardless of whether Floating IP is enabled
  17. elishlomo 👍 2 Answered A
    A. If you want to use the backend port across multiple rules, you must enable Floating IP in the rule definition.
  18. Naru60 👍 2 Answered A
    Floating IP (Direct Server Return) must be enabled if ILB is used for SQL Server Always On listeners.
  19. happpieee 👍 2
    Yes floating IP is a configuration supported by Azure LB:
  20. Nico1973 👍 1
    Answer: B. No Explanation: Enabling Floating IP is not the correct solution for configuring an Azure internal load balancer as a listener for the availability group. In Azure, for an internal load balancer to act as a listener for the availability group, you should configure the load balancer with a Standard SKU and a Basic SKU public IP address. The internal load balancer should be associated with the back-end pool of the availability group nodes. Therefore, enabling Floating IP does not meet the goal of configuring an Azure internal load balancer as a listener for the availability group.
  21. LPaul 👍 1
    The ILB listener uses a health probe to determine if the primary endpoint is down. If the health probe determines that the primary endpoint is down, the ILB listener will route traffic to the secondary endpoint. The health probe sends a request to the primary endpoint and waits for a response. If the response is not received within a specified time period, the health probe determines that the primary endpoint is down and routes traffic to the secondary endpoint
  22. ra_ste_ele 👍 1 Answered B
    IP mobile è un concetto usato per ambiente on-premises o in contesti con failover IP tra nodi. In Azure, il listener per un gruppo di disponibilità non funziona automaticamente con IP mobile perché: Azure non supporta IP fluttuanti tra VM come in ambienti fisici. Il traffico in Azure deve essere gestito tramite Load Balancer, non tramite IP trasferibili.
  23. eddzequiel 👍 1
    worksThe load balancing rules configure how the load balancer routes traffic to the SQL Server instances. For this load balancer, you enable direct server return because only one of the two SQL Server instances owns the availability group listener resource at a time.
  24. thalasi 👍 1 Answered A
    Required settings Internal Load Balancer (ILB) Protocol: TCP Health probe: Type: TCP Port: Custom (example: 59999) Session persistence: None Floating IP (DSR): Enabled Backend pool: All SQL AG nodes Listener port mappings: Frontend port: 1433 Backend port: 1433
  25. BiniJacob 👍 1 Answered B
    While enabling Floating IP (Direct Server Return) is a critical and required step for configuring a SQL Server Always On availability group listener on an Azure internal load balancer, it is only a single part of the larger solution

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