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: Juniper Networks (Nasdaq: JNPR) dropped 21% in intraday trading today after the networking equipment maker reported disappointing preliminary earnings and guidance; at least 10 analysts lowered their ratings on the stock.

So what: For the second quarter, non-GAAP EPS of $0.31 missed the $0.34 consensus estimate and increased only 3% year over year. GAAP EPS declined 11% year over year to $0.21. Revenue increased 15% to $1.12 billion, falling short of the $1.15 billion consensus forecast.

Now what: The company said the disappointing results and outlook were the result of, "[A] number of factors ... including mixed signals in the macro economy ..." It emphasized expense control measures to cope with the near-term environment and new products aimed at improving results over the long term, suggesting management doesn't expect near-term improvements. Juniper guided third quarter non-GAAP EPS to $0.26-$0.30 and revenue to $1.07 billion-$1.12 billion. Both are well below consensus expectations for non-GAAP EPS of $0.38 and revenue of $1.22 billion. The negative comments from Juniper are also pressuring stocks of competitors Alcatel-Lucent (NYSE: ALU), Cisco Systems (Nasdaq: CSCO), and CIENA (Nasdaq: CIEN), indicating investors are concerned about overall demand and do not believe Juniper's troubles are company specific.