I wrote a REST service to call another system from Salesforce. They have firewalls up and such and I instructed them to Whitelist the following:

204.14.232.0/23 East Coast Data Center (set one)
204.14.237.0/24 East Coast Data Center (set two)
96.43.144.0/22  MidWest Data Centers
96.43.148.0/22  MidWest Data Centers
204.14.234.0/23 West Coast Data Center (set one)
204.14.238.0/23 West Coast Data Center (set two)
202.129.242.0/23 Singapore Data Center
182.50.76.0/22 Japan Data Center

The return I am getting is:

<status type="Error" code="LoginError" message="Invalid stored procedure name ''." />

They asked me to get the exact IP Salesforce is calling from. From what I understand this isn't possible, but am I incorrect? If I am incorrect how do I find it?