Cisco Systems Inc., the largest maker of computer networking equipment, plunged in late trading after giving a disappointing forecast, adding to concern that corporations are reining in their technology spending.

Sales will be $12.6 billion to $12.8 billion in the period ending in January, the company said in a statement Wednesday. That was far short of the $14.2 billion analysts had estimated. Excluding certain items, profit will be 82 cents to 84 cents a share, compared with a prediction of 99 cents.