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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