When working with enterprise web applications, developers often need to handle multiple subdomains pointing to the same application. Prior to IIS 8.5, administrators had to manually create individual bindings for each subdomain (e.g., www.example.com, api.example.com, blog.example.com), which became tedious in large-scale deployments.

Yes, IIS 8.5 (shipped with Windows Server 2012 R2) does support wildcard host header bindings. This is particularly useful when combined with SNI (Server Name Indication) for SSL certificates. Here's how the binding configuration works:

<bindings>
    <binding protocol="http" bindingInformation="*:80:*.example.com" />
    <binding protocol="https" bindingInformation="*:443:*.example.com" sslFlags="1" />
</bindings>

To set up wildcard bindings programmatically using PowerShell:

Import-Module WebAdministration
New-WebBinding -Name "Default Web Site" -IPAddress "*" -Port 80 -HostHeader "*.example.com" -Protocol "http"
New-WebBinding -Name "Default Web Site" -IPAddress "*" -Port 443 -HostHeader "*.example.com" -Protocol "https" -SslFlags 1

For applications needing to handle the wildcard domain in code, you can access the host header in ASP.NET:

protected void Application_BeginRequest(object sender, EventArgs e)
{
    string host = Request.Headers["Host"];
    if (host.EndsWith(".example.com"))
    {
        // Handle subdomain logic
    }
}

• Wildcard bindings work with both HTTP and HTTPS (when using SNI)
• SSL certificates must support wildcard domains (*.example.com)
• IIS 8.5 handles the binding precedence correctly when mixing specific and wildcard bindings
• Application Request Routing (ARR) can complement this feature for more complex routing needs

Unlike IIS 7.5 which required URL rewrite rules as workarounds, IIS 8.5 provides native support with better performance and simpler configuration. The feature was introduced alongside other improvements in the HTTP.sys stack.

With IIS 8.5's introduction of Server Name Indication (SNI) support, many administrators expected wildcard host header binding to follow naturally. While earlier versions (7.5 and below) strictly required explicit domain listings, the situation has evolved in subtle ways.

Microsoft's documentation remains silent about wildcard (*.domain.com) support in host headers, but practical testing reveals partial functionality when combined with specific configurations:

// PowerShell binding example
Add-WebBinding -Name "Default Web Site" -IP "*" -Port 443 -HostHeader "*.example.com" -Protocol "https"

While SNI enables multiple SSL certificates on a single IP, it doesn't automatically enable wildcard host headers. However, IIS 8.5's enhanced certificate handling creates interesting possibilities:

// ApplicationHost.config snippet
<binding protocol="https" bindingInformation="*:443:*.devcorp.net" certificateHash="..." />

For scenarios requiring true wildcard handling, consider these approaches:

• URL Rewrite module patterns
• Centralized certificate store with pattern matching
• Application-level routing

// Web.config rewrite rule
<rule name="Wildcard Subdomain" patternSyntax="Wildcard">
  <match url="*" />
  <conditions>
    <add input="{HTTP_HOST}" pattern="*.example.com" />
  </conditions>
  <action type="Rewrite" url="/{C:1}/{R:0}" />
</rule>

Benchmark tests show that explicit bindings outperform wildcard attempts by 12-15% in request processing. The tradeoff between maintenance overhead and performance should guide implementation decisions.

With IIS 10's enhancements to containerization and cloud scenarios, wildcard handling may see official support. Current architectural constraints in the HTTP.sys kernel-mode driver remain the primary limiting factor.