How To force curl to use only one network interface.
First, determine which interact your IP address is on. The easiest way to determine is to find the IP address and see the interface. Use this API call to see the public_ip and the interface.
# whmapi1 listips
Second, use the "--interface " option with curl.
# curl --interface eeth0:cp1 https://cpanel.net/showip.shtml