Port issue on binding

Scott Huang 3,511 Reputation points
2026-03-21T08:22:10.4166667+00:00

Hi,

On IIS binding, both of the 2 sites are running on port 443. Both of them cannot be up at the same time as they're all on port 443. I want to switch one of them to port 4431 (or any other option you can advise). Can you help?

Developer technologies | ASP.NET Core | Other
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Jack Dang (WICLOUD CORPORATION) 18,980 Reputation points Microsoft External Staff Moderator
2026-03-23T06:48:11.7433333+00:00

Hi @Scott Huang ,

Thanks for reaching out.

Regarding your concern, instead of creating something like abc2.com, you can set up the second site as an application (or subsite) under your main site. This would give you URLs like:

https://abc.com/s1
https://abc.com/s2

A few important points:

  • These are paths under the same host, not separate host names.
  • IIS routes requests to the correct application based on the URL path, so each subsite behaves like a separate website even though they share the same domain and port.
  • Both subsites can run on port 443, and typically one SSL certificate is sufficient if it covers your main domain.

For completeness, another option (as Bruce mentioned) is to use different host names on port 443. That also works, but since you want to avoid multiple domains, the application/path approach is usually simpler.

Hope this helps! If my answer was helpful, I would greatly appreciate it if you could follow the instructions here so others with the same problem can benefit as well.

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  1. Bruce (SqlWork.com) 85,416 Reputation points
    2026-03-21T14:55:29.8833333+00:00

    With IIS all ssl sites can use port 443. If two site are root sites, then they should have different host headers (dns name). They can also be sub sites (applications) of the same root site.

    samples that can coexist:

    https://site1.abc.com

    https://site2.abc.com

    https://abc.com/site1

    https://abc.com/site2

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  2. AI answer

    2026-03-21T08:22:23.0866667+00:00

    Both sites can’t share the same IP + port 443 for SSL unless using SNI correctly. To have them up at the same time without changing certificates or SNI, change one site’s HTTPS binding to a different port and update any clients to use that port.

    Steps to move one site from 443 to 4431 (example):

    1. Open IIS Manager.
    2. In Connections, expand the server node and select the site that should move off 443.
    3. In the Actions pane, select Bindings….
    4. Select the https binding on port 443 and click Edit….
    5. Change Port from 443 to 4431 (or another free port).
    6. Ensure the correct SSL certificate is still selected.
    7. Click OK, then Close.
    8. Restart that site.
    9. Access it using the new URL, for example:
      • https://yourdomain:4431/

    Key points and options:

    • Only one site can bind to the same IP:443 for SSL unless using Server Name Indication (SNI). Without SNI, IIS cannot distinguish sites by host header for SSL, so a second site on the same IP:443 will fail to bind.
    • Using a nonstandard SSL port (like 4431) is valid, but clients must include the port in the URL and any firewalls must allow that port.
    • Alternatively, if multiple IP addresses are available, assign different IPs so each site can keep port 443 (for example, Site A on 192.168.0.10:443 and Site B on 192.168.0.11:443).

    If the environment supports IIS 8 or later and both sites use compatible certificates, enabling SNI on the HTTPS bindings is another way to host multiple SSL sites on port 443 using different host names.

    References:

    AI-generated content may be incorrect. Read our transparency notes for more information.

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