Lot’s of good stuff here. I don’t have time to reference individual quotes from specific posters. But here are some key points.
(a) Internet vs. Intranet. If you’re strictly concerned about a network protocol, it’s irrelevant whether IP is implemented on the Internet or an intranet. Internet Protocol does not imply that it refers to the Internet. It's just the name of the protocol (talking just network layer protocol here as in the original post). Most of the time I just use “data network”, or “packet data network” if I need to distinguish between “circuit-switched” and “packet-switched”. The distinction between Internet vs. intranet will often arise in applications on secure access and firewalls. Most of the time, I just use “a first domain” and “a second domain” and access permissions between them. Why reference the nebulous “Internet” if you don’t have to?
(b) OSI Layers. There’s a classic text by Tannenbaum on computer networks. In one edition, he declared the OSI model to be a failure. One of the most common architectures in use is TCP (or UDP) over IP over Ethernet. This does not map directly into the OSI model. The Ethernet MAC layer is sometimes referred to as layer 2.5, whatever that means. And I’ve yet to come across practical instances of layer 5 and layer 6.
(c) Standards and Quasi-Standards. If you state that the Internet Protocol requires no further clarification, then it’s really because you are implicitly falling back on a reference to a standard or quasi-standard such as an RFC. This also holds true for FTP, HTTP, SIP, Ethernet. You then run into the tricky bind of unnecessarily limiting yourself to a particular standard (especially when a standard is abandoned and replaced by another one). If an Examiner issues a 112 because “IP” is indefinite for lack of written description, are you going to respond that IP has a well-known dictionary (=RFC in this case) definition?
(d) As usual, the context is critical.
What if the prior art is IPv4, and the invention is IPv6? What is the (or an) IP address? Well, for IPv4 it is a 32-bit address. The well known problem is that there aren’t enough addresses to go around, so one feature of IPv6 is to expand the address space to 128 bits. Do you want your claims to cover other hypo network routing protocols that use an n-bit address space?
Similarly, what is Ethernet? Is Ethernet well-defined outside of IEEE 802? It has evolved from 802.0X to 802.11X. Are you interested in the physical layer aspects (thicknet vs thinnet vs twisted pair vs wireless)? If the invention is Ethernet transport over a new media (e.g., free-space optics), do you want your claims to cover other hypo protocols over new physical media? Are you interested in multiple access and collision detection? If the invention is an improved method for reducing the probability of collisions on second and subsequent re-transmission attempts, do you want your claims to cover other hypo non-802 MAC layer protocols that use multiple access and collision detection?
Added: There are at least two file transfer protocols, FTP and TFTP; don't know if there are others. So, again, you need to be careful about what "file transfer protocol" refers to. What aspects are the claims actually using?
(e) Even with "North Pole" the situation isn't all that straightforward. There is a "geographical North Pole" and a "magnetic North Pole". Furthermore, the magnetic North Pole is not fixed relative to the geographical North Pole. So, we actually have a plurality of magnetic North Poles as a function of time. If my invention concerns a correction factor for navigation instruments, I would need to maintain this distinction. For that matter, I think the geographical North Pole varies with time relative to some celestial reference frame, but the details are too hazy for me now.