In fact, HP is shaping up to be not just a competitor, but Cisco's biggest rival, Schuchart said. With its acquisition of 3Com, expected to close by midyear, the company will have a fairly complete lineup of both routing and switching products, though not quite the same breadth as Cisco, he said. While Cisco had more than two-thirds of the Ethernet switch market in the third quarter of last year, HP and 3Com were the second- and third-place vendors in that business, with a combined 10.3 percent of the market, according to figures from Dell'Oro Group.

Both companies are likely to continue building their forces through acquisitions, UBS Warburg analyst Nikos Theodosopoulos wrote in a research note. "We expect the competition between Cisco and HP to be intense over the next few years," he wrote. They are likely to use aggressive financing deals to win customers, he wrote.

As HP bulks up to take ground from Cisco, the latest development hurts it more, according to a research note by Ovum. "It appears that HP needs Cisco more than Cisco needs HP, with the 3Com acquisition expected to still take some time to be completely integrated," the analyst company said.

However, both Cisco and HP are smart enough not to let their rivalry hurt customers who bought into the two vendors in happier times, analysts said.

"Customers will not be forced to choose between one and the other," Schuchart said. However, "They might be asked," he added.