Sometimes you need to quickly identify the ip addresses from which proxy requests will come in to your back end services. Perhaps you need to scan logs to identify requests, etc. The definitive way to get this information is to contact support, but for a quick-and-dirty answer you can create a simple pass-through proxy to http://httpbin.org/ip.
Then simply make a few requests to your new proxy, and you'll see the IP addresses. These may change over time (hence contact support for best answer), but for a "one minute" answer this is pretty quick.
☯ http http://cdmo-prod.apigee.net/ip HTTP/1.1 200 OK Access-Control-Allow-Credentials: true Access-Control-Allow-Origin: * Connection: keep-alive Content-Length: 33 Content-Type: application/json Date: Thu, 12 Feb 2015 22:51:10 GMT Server: nginx { "origin": "107.23.127.110" } ☯ http http://cdmo-prod.apigee.net/ip HTTP/1.1 200 OK Access-Control-Allow-Credentials: true Access-Control-Allow-Origin: * Connection: keep-alive Content-Length: 32 Content-Type: application/json Date: Thu, 12 Feb 2015 22:51:12 GMT Server: nginx { "origin": "107.23.127.33" }