sayantansinha,
[Sorry, I typed this but forgot to send it.]
Yes, indeed, Angular IDE supports Angular 6. Angular 6 changed the name of the Angular CLI json file, which meant it wasn’t recognized by our tooling as an Angular project and so didn’t appear in the Angular CLI servers view. We fixed that in an older release than the one you have and, as you see, it appears in the servers view now.
This may require a call to sort out but can you confirm that you are able to use all other angular tools in eclipse and run npm update from the Terminal+ view? I’m asking only because you mentioned upgrading to Angular 6 outside of eclipse so I just want to make sure that you do use the Angular IDE facilities for most of the development. If so, then we need to figure out why your getting issues that appear to be network related when there is nothing wrong with your network set up in eclipse.