As mentioned on the NowSMS documentation, the MMSC works best with operator WAP gateways when it is configured to use HTTP port 80. HTTP Port 80 is the standard port used by web servers. If an IIS web server is running on the same PC as the NowSMS gateway, it is likely that port 80 is already in use by the IIS web server.
If you can bind multiple IP addresses to the PC running IIS and the NowSMS gateway, it is possible for both IIS and NowSMS to use port 80, by assigning one IP address to IIS, and another IIS to the NowSMS gateway.
To assign a specific IP address to the NowSMS gateway, it is a simple matter of selecting the appropriate IP Address from the “IP Address” list on the MMSC configuration dialog. This setting defaults to “(all available)”, meaning that the NowSMS gateway would bind to the specified ports on all IP addresses bound to the PC. Note that when you configure NowSMS to use a specific IP address, it will no longer be accessible on the local machine using the loop back address 127.0.0.1, you must always use the specific IP address, even when connecting from the local machine. Also note that the “IP Address” setting on the MMSC configuration dialog applies only for the IP address used by the HTTP and SMTP ports of the MMSC. The NowSMS gateway itself also has an HTTP web port. The IP address setting for that interface is found on the “Web” configuration dialog.
It is not as simple to configure IIS to bind to only a specific IP address. IIS has a feature called “socket pooling”, which causes it to grab the web ports on all IP addresses configured on the machine, even if web services have only been configured for a specific IP address.
To configure IIS to bind only to a specific IP address or a limited number of specific IP addresses, check the configuration of each host defined in the Internet Information Services Manager, and ensure that the host is configured for a specific address instead of all unassigned addresses. You must then disable IIS socket pooling.
For information on disabling socket pooling on IIS, and configuring IIS to connect to only a specific IP address, please consult the following Microsoft references:
IIS Binds To All Available IP Addresses When It Starts
How to Disable Socket Pooling
XCON: How to Disable Internet Information Services Socket Pooling on the SMTP Service
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