We are using a HTTP Restful Outbound Webservice which was working fine for 2 years but suddenly stopped working which we are not able to understand the reason. It's giving below error.
System.CalloutException: Unable to tunnel through proxy. Proxy returns "HTTP/1.0 404 Not Found"
It looks like Firewall issue to us, but our internal Network team is claiming that, the inbound request from Salesforce is not reaching our Firewall as per logs though IP's provided by Salesforce are correctly whitelisted. But this is working in Sandboxes so we don't think it's Salesforce issue. I would like to know if there is a tool or by any means, can we ping our ESB servers from Salesforce instance?
public class postCall(String siebelId ){
Http h = new Http();
HttpRequest req = new HttpRequest();
req.setEndpoint('https://esb.ent.abc.org/ServiceRequest');
req.setMethod('POST');
req.setBody('{"ocl:accountId":"'+siebelId+'"}');
req.setHeader('Token', '9fdb3ab5-efc8-473f-bc5e-a474b0b9d1e2');
HttpResponse res = h.send(req);
System.debug(res.getBody());
}