Load balancing On Premises Layer 4 ports(smtp) with Azure VM

BUDHADITYA BANERJEE 71

Load Balancing On Premises Layer 4 ports(smtp) with Azure VM

We do have On Prem exchange environment which we want to replicate to Azure VM using Azure Site recovery. During initial timeframe, I need to do run Exchange with Hybrid mode(Active Active On-prem with Azure VM). I am aware of Layer 7 solutions of Application Gateway or Frontdoor or Traffic Manager but unable to find any Layer 4 solution with Azure.

Please note that i dont want to use Exchange Active manager as my DNS will route the traffic to the Global Load Balancer or any other FrontEnd appropriate load balancing solution in Azure which will route the traffic to On Prem or Azure VM backend as per the load balancing strategy.

Prrudram-MSFT 22,391 Reputation points

2023-03-13T18:42:43.6166667+00:00

Hi @BUDHADITYA BANERJEE

Thank you for reaching out to the Microsoft Q&A platform.

Azure Load Balancer provides layer four load balancing for TCP and UDP traffic. You can use Azure Load Balancer to balance the SMTP traffic between your on-premises environment and Azure VM.

To configure layer four load balancing for SMTP traffic, you need to create a load balancer with a public IP address and configure load balancing rules to map the front-end IP and port combination to a set of back-end IP addresses and port combination associated with your on-premises environment and Azure VM. You can also configure probes to monitor the health of your on-premises environment and Azure VM and ensure that only healthy servers receive connection requests.

For more information on how to configure layer four load balancing with Azure Load Balancer, see the Azure Load Balancer documentation: https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-overview
Prrudram-MSFT 22,391 Reputation points

2023-03-13T18:43:17.16+00:00

@BUDHADITYA BANERJEE

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BUDHADITYA BANERJEE 71 Reputation points

2023-03-15T09:55:56.01+00:00

Hello @Prrudram-MSFT , Thanks a lot for the inputs. Will it be possible to use the regional Load balancer to load balance on-prem VM and Azure VM for Layer 4 traffic? Please confirm as when i was checking the KBs, i found that Layer 4 load balancers cannot load balance OnPrem with Azure. Azure Cross Region load balancer(preview) do have the capability to load balance Layer 4 traffic between multiple Azure regions only. That also only TCP traffic not UDP.

Please confirm as this will be helpful for me to get into a solution accordingly.

Thanks,

Aditya.

1 answer

msrini-MSFT 9,261 Reputation points Microsoft Employee

2023-03-10T19:35:14.9133333+00:00

Hi,

You cannot use the On-Prem Server as backend pool of Azure Load balancer (layer 4)as of today.

You will need to go with Application Gateway or Azure Frontdoor.

Regards,

Karthik Srinivas
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BUDHADITYA BANERJEE 71 Reputation points

2023-03-15T10:02:19.7833333+00:00

@msrini-MSFT Hello Karthik,

Thanks a lot for taking out sometime and providing the inputs. Problem with App Gateway and FD is, they do have Layer 7 capabilities. But here i want SMTP/POP/IMAP3 Layer4 ports to be load-balanced. Is there any solution in Azure to achieve that?

Also, one more input needed here, As the Global Load balancer is currently in preview, is there any other alternative to load balance layer4 traffic between multiple Azure regions?

Thanks,

Aditya.

msrini-MSFT 9,261 Reputation points Microsoft Employee

2023-03-20T18:58:46.5766667+00:00

Unfortunately with layer 4 LB, you cannot load balance traffic with On-Premises as of today
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