Merge pull request #87375 from mazgi/patch-1

Update Firewall SNAT ports limit 1024 -> 2496

Author: ktoliver

articles/firewall/overview.md

@@ -81,7 +81,7 @@ Azure Firewall Standard has the following known issues:
 |SNAT on inbound connections|In addition to DNAT, connections via the firewall public IP address (inbound) are SNATed to one of the firewall private IPs. This requirement today (also for Active/Active NVAs) to ensure symmetric routing.|To preserve the original source for HTTP/S, consider using [XFF](https://en.wikipedia.org/wiki/X-Forwarded-For) headers. For example, use a service such as [Azure Front Door](../frontdoor/front-door-http-headers-protocol.md#front-door-to-backend) or [Azure Application Gateway](../application-gateway/rewrite-http-headers-url.md) in front of the firewall. You can also add WAF as part of Azure Front Door and chain to the firewall.
 |SQL FQDN filtering support only in proxy mode (port 1433)|For Azure SQL Database, Azure Synapse Analytics, and Azure SQL Managed Instance:<br><br>SQL FQDN filtering is supported in proxy-mode only (port 1433).<br><br>For Azure SQL IaaS:<br><br>If you're using non-standard ports, you can specify those ports in the application rules.|For SQL in redirect mode (the default if connecting from within Azure), you can instead filter access using the SQL service tag as part of Azure Firewall network rules.
 |Outbound SMTP traffic on TCP port 25 is blocked|Outbound email messages that are sent directly to external domains (like `outlook.com` and `gmail.com`) on TCP port 25 are blocked by Azure Firewall. This is the default platform behavior in Azure. |Use authenticated SMTP relay services, which typically connect through TCP port 587, but also supports other ports.  For more information, see [Troubleshoot outbound SMTP connectivity problems in Azure](../virtual-network/troubleshoot-outbound-smtp-connectivity.md). Currently, Azure Firewall may be able to communicate to public IPs by using outbound TCP 25, but it's not guaranteed to work, and it's not supported for all subscription types. For private IPs like virtual networks, VPNs, and Azure ExpressRoute, Azure Firewall supports an outbound connection of TCP port 25.
-|SNAT port exhaustion|Azure Firewall currently supports 1024 ports per Public IP address per backend virtual machine scale set instance. By default, there are two virtual machine scale set instances.|This is an SLB limitation and we are constantly looking for opportunities to increase the limits. In the meantime, it is recommended to configure Azure Firewall deployments with a minimum of five public IP addresses for deployments susceptible to SNAT exhaustion. This increases the SNAT ports available by five times. Allocate from an IP address prefix to simplify downstream permissions.|
+|SNAT port exhaustion|Azure Firewall currently supports 2496 ports per Public IP address per backend virtual machine scale set instance. By default, there are two virtual machine scale set instances. So, there are 4992 ports per flow (destination IP, destination port and protocol (TCP or UDP).  The firewall scales up to a maximum of 20 instances. |This is a platform limitation. You can work around the limits by configuring Azure Firewall deployments with a minimum of five public IP addresses for deployments susceptible to SNAT exhaustion. This increases the SNAT ports available by five times. Allocate from an IP address prefix to simplify downstream permissions. For a more permanent solution, you can deploy a NAT gateway to overcome the SNAT port limits. This approach is supported for VNET deployments. <br /><br /> For more information, see [Scale SNAT ports with Azure Virtual Network NAT](integrate-with-nat-gateway.md).|
 |DNAT isn't supported with Forced Tunneling enabled|Firewalls deployed with Forced Tunneling enabled can't support inbound access from the Internet because of asymmetric routing.|This is by design because of asymmetric routing. The return path for inbound connections goes via the on-premises firewall, which hasn't seen the connection established.
 |Outbound Passive FTP may not work for Firewalls with multiple public IP addresses, depending on your FTP server configuration.|Passive FTP establishes different connections for control and data channels. When a Firewall with multiple public IP addresses sends data outbound, it randomly selects one of its public IP addresses for the source IP address. FTP may fail when data and control channels use different source IP addresses, depending on your FTP server configuration.|An explicit SNAT configuration is planned. In the meantime, you can configure your FTP server to accept data and control channels from different source IP addresses (see [an example for  IIS](/iis/configuration/system.applicationhost/sites/sitedefaults/ftpserver/security/datachannelsecurity)). Alternatively, consider using a single IP address in this situation.|
 |Inbound Passive FTP may not work depending on your FTP server configuration |Passive FTP establishes different connections for control and data channels. Inbound connections on Azure Firewall are SNATed to one of the firewall private IP addresses to ensure symmetric routing. FTP may fail when data and control channels use different source IP addresses, depending on your FTP server configuration.|Preserving the original source IP address is being investigated. In the meantime, you can configure your FTP server to accept data and control channels from different source IP addresses.|