My apologies if this forum is inappropriate as this question may even be beyond the scope of this community but I figured it wouldn't because you guys have been so helpful to me in the past (how's that for a suck up?) .

My job is working in advanced server support for a UK government department ... actually I'm outsourced (work for another company contracted to provide a specific service to the department) but that seems to be the way these days.

As sees to be typical there are several levels of support usually contacted before me and my colleagues but one thing seems to be true; because users always perceive problems from the POV of their own PC and its ability to access varied network resources we (server and/or desktop support) are always the first point of contact. As such, in the event that we begin to suspect that the problem lies outside of our domain (not a Windows domain although those are involved), it becomes our responsibility to *prove* that it's another aspect of the network or service because if we suggest that to other teams the usual response is "there's nothing wrong with <XXXX> ... " and so on. IMO that's not the way it should be but it invariably seems to be (is even understandable form a customer perspective) and it also tends to mean we get the flack (irritable and sometimes even angry customers).

The trouble is, of course, that whilst I know a lot about servers, and a fair bit about networks in general, I am by no means a LAN/WAN expert, what I know about Cisco switches could be written on a pinhead and I have no specific method for establishing that an issue lies outside our domain. I think I need such a method so I've decided to create a document (an aide memoire or checklist) for my own use in the first instance but for the team perhaps later on so, if required, I can firmly establish where the fault lies, if it is a server issue, a router, a switch or whatever.

What steps should I take? What things should I check? What are the implications of various bits of information if known? Does anyone have any really good resources that they can point me to so I can create the document I want to? Any help on this would be most definitely appreciated.