Cisco's the king of network security, commanding almost a quarter share of the worldwide $6.8 billion network security market, according to IDC. But can it hold the fort?

Tops in selling firewalls, VPNs, intrusion-protection systems and unified threat management (UTM) gear, Cisco nonetheless fights an ongoing battle to be recognized as best-of-breed as it jousts against Juniper and a host of pure-play security vendors, including Fortinet, McAfee and TippingPoint.

Complicating matters is the fact that Cisco sells a substantial portion of its security wares not as purpose-built standalone gear, such as appliances, but as software integrated-services modules that are installed inside Cisco routers and switches.

Click to see: Pie charts showing various markets Cisco is leading in most of.

While all customer networks have different traffic patterns, there's growing doubt about how well these firewall, VPN and IPS modules hold up trying to handle process-intensive security functions.

"It presents a tremendous bottleneck," says Vik Phatak, chair and CEO of NSS Labs, which has just completed an extensive round of tests of security gear, including that from Cisco, Juniper, IBM, McAfee, and TippingPoint, in its Austin-based labs.

NSS Labs will publish its findings about firewalls, IPS and UTM early next year, but Phatak says he has concluded that there are clearly performance drawbacks to using the Cisco security functions in routers and switches.

"Using IPS in your router can turn a 60G router into a 5G one or even a 100M bit/sec device," says Phatak. "There are performance bottlenecks." He adds that sometimes security functions simply can't keep up when speeds are high.

But Phatak also points out that the tests of Cisco's standalone security appliances fared quite well against its rivals' equipment in the NSS Labs environment, which included simulation of perimeter, internal network and e-commerce. "TippingPoint, McAfee, Juniper, Cisco and IBM are all 'Grade A,' " Phatak says.

Click to see: Pie chart indicating Cisco's lead in the network security market

Cisco says the effectiveness of the software-based security modules in routers and switches depends on the use case, and it helps customers work out any problems that crop up. Cisco indicated its network security sales are split fairly evenly between the modules and appliances. And there are no plans to change the integrated security services strategy.