The answer, of course, is that it depends upon what you're trying to do. The optimal Linux networking setup is the one that you tailor to meet the needs of your environment! Seriously, it's difficult for me to answer this because I like to think that almost all of the Linux networking environments I've worked with have been optimal in one sense or another.
Optimal to me means that you have redundant hardware where it's needed, particularly when it comes to hard drives and power supplies. It also implies good server room environmentals; namely, environments that have power and air conditioning, and a well-tuned monitoring and notification environment. There should also be an adequate lab environment and time enough for the IT team to make use of it, so that you're not 'trying' things in production.
Optimal also means a management team that is willing to trust the judgment of its employees over the four-colored glossies being peddled by ABC Sales Dude.
You need all that, plus lots of blinky lights and little penguin stickers to put on all of the machines. What new networking technologies are coming, and how will they help businesses?
IPv6, although not exactly new, is still coming. It will be a great boon to businesses because it greatly simplifies the need for IP address management. DHCP and NAT have done a lot to increase the useful life of IPv4, but they've also created a fair
VoIP (Voice over IP), although also not exactly new, is already here, but it's not widely used and needs technology development. It will be the sledgehammer to bring down the 'Berlin Wall' erected by AT&T and all of the other proprietary telco vendors over the years.
Having a powerful general purpose computer on your desk, while still having a separate telephone and voicemail system, is just plain wasteful. VoIP is delay-sensitive, and so it requires networks that can categorize traffic according to well-defined priority. The need for this will drive a host of related technologies, such as QoS and ATM. How about Wi-Fi (wireless fidelity)?
Wi-Fi and other wireless technologies are also just about here, but I think that the potential for wide-scale deployment hasn't even begun to be tapped. For anyone who's been involved with managing a network build-out, you know that wiring is expensive, and re-wiring is doubly so. The ability to drop workstations anywhere that a power outlet is available (which implies that your phone extension will be delivered via VoIP) will enable businesses to save and be much more nimble.
For more information:
Linux networking tips: Practical Guide to Red Hat Linux, Chapter 9