I am trying to make an apex callout from salesforce to the external system which is hosted inside in corporate firewall. Firewall sends the request to load-balancer which sends the request to appropriate web server.

I am getting below exception when trying this call from salesforce while I can getting the correct response while making a callout from SOAP UI.

As per my client, they don't provide any certificate. I am not sure what is happening and how to resolve the issue. As per few blogs, it seems like I need to install the certificates.

Any help would be appreciated.

Log -

[51]|System.HttpRequest[Endpoint=https://someURL/servlet/request, Method=POST] 07:51:12.268 (268755208)|CALLOUT_REQUEST|[51]|System.HttpRequest retrying request in response to handshake failure: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target 07:51:12.423 (423017546)|EXCEPTION_THROWN|[51]|System.CalloutException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target 07:51:12.423 (423110461)|SYSTEM_METHOD_EXIT|[51]|System.Http.send(ANY)