Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of network equipment maker Ixia (Nasdaq: XXIA) plunged more than 25% after reporting lower second-quarter guidance last night.

So what: Management said economic conditions in Asia and late orders from major clients depressed demand that had been strong in prior quarters. Revenue was up 38% in the fourth quarter and 26% in the first. For the second quarter, revenue is now expected to come in between $67 million and $69 million, a barely noticeable uptick from year's $66 million and down sharply from earlier estimates of $78 million to $82 million.

Now what: You'd think that Ixia's application performance gear -- used to help test data delivery over Internet, 3G, and LTE networks, specifically -- would still be in high demand. The numbers say otherwise. Though to be fair, Ixia says it met its fulfillment obligations to Cisco (Nasdaq: CSCO), its largest customer, which accounted for 13.5% of last year's revenue. But Cisco is also just one customer, and given the size of the shift in guidance, there appear to be plenty of others who hold a little too much sway over Ixia's fortunes. Tread carefully here, Fool.

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Fool contributorTim Beyers is a member of theMotley Fool Rule Breakers stock-picking team. He didn't own shares in any of the companies mentioned in this article at the time of publication. Check out Tim'sportfolio holdings andFoolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insightsdelivered directly to your RSS reader.

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