Cisco Systems (CSCO) has long had a unique competitive position in the enterprise market. In the glory days of the mainframe, IBM still competed with HDS and Amdahl, but Cisco has had the enterprise networking market to itself for a number of years.

This monopoly seems to be at its greatest risk ever — ESG calls this market phenomenon the Cisco squeeze. Think of Cisco in the middle of a big triangle with the competition closing in on Cisco from three distinct fronts:

1. Innovation. Juniper’s (JNPR) Trio chipset and 3-D architecture set a new plateau for networking performance that Cisco can’t match. Yes, this is probably a bigger threat in the service provider market than the enterprise, but large enterprises like DISA and NYSE are buying into Juniper innovation. Beyond Juniper, companies like F5 Networks (FFIV), Citrix (CTSX), and Riverbed (RVBD) are out innovating Cisco in strategic areas as well. Finally, small enterprises are looking longer at innovative and affordable alternatives like Extreme Networks (EXTR), Force10, and even 3Com (COMS) to get better end-to-end functionality at a lower price point.

2. Commodification. While aggressive innovators hurt Cisco at the high margin data center and core network, commodification hurts Cisco at the edge. The best example here is HP. Low-cost edge and wiring closet switches with lifetime warranties are increasingly “good enough” for many Cisco customers. If history repeats itself and the low end scales to eat the high end, HP (HOQ), Dell (DELL), and other commodity networking vendors will continue to gain share at Cisco’s expense.

3. Server vendors. With its introduction of UCS (aka: California), Cisco effectively alienated major partners Dell, HP, and IBM (IBM). Publicly each of these companies say that they will continue to work with Cisco but privately they are mobilizing the troops. Both Dell and IBM now OEM networking equipment from Brocade (BRCD)and Juniper while HP is bolstering its ProCurve offerings with new products and partners. The rumor is that HP will no longer pay its sales reps commission on selling Cisco gear — that will certainly change selling behavior.

Cisco is a huge successful company with good products, great support, and some of the best sales and marketing in the industry. It also has done a great job diversifying into new areas like Telepresence, consumer electronics, unified messaging, and yes, even servers. Cisco is a machine that will continue to flourish but it clearly faces greater competitive and market pressures today than ever before.

Here are a few things I’ll be watching for over the next few quarters:

1. Layoffs or budget cuts in sales, marketing, or field support. This will tell me that margins are eroding, existing field skills are no longer useful, or Cisco is losing strategic battles.

2. “Back to basics” messages from John Chambers. If the ever-visionary Cisco CEO starts speaking to Wall Street in cliches like, “we took our eye off the ball,” or “we need to get back to basic blocking and tackling,” things are way worse than most people think.

3. Big acquisitions. If Cisco goes out and buys an F5 Networks, Riverbed, or ArcSight (ARST), it tells me that internal innovation can no longer keep up with the market.

4. Server deals. If Cisco wins large UCS deals, everything else will come along for the ride. If not, everything else will be challenged.

5. HP. If HP develops or acquires high-end networking equipment and new enterprise boss Dave Donatelli can instill an EMC-like sales culture at HP, Cisco will have its hands full.

Innovation, comodification, and competition are at the heart of the tech industry. Most industry leaders face these challenges from day one but Cisco through a combination of skill, luck, and lack of true competitors was able to tap dance around these pressures for a long time but no longer. Over the next few years, Cisco will be challenged like never before. It will certainly be interesting to see how it all unfolds.