Cisco's IOS vs Juniper's JUNOS

"We need to be able to [assure] three different constituencies - demo, production and engineering - that [converged voice, video and data] will work well across one environment," Noga said. "As we moved around [between departments], we continued to understand the operating system."

Understanding the operating system is key for Cisco shop FactSet Research Systems as well. The company is a provider of financial information and analytic applications for worldwide investors that is consolidating several older Cisco 7200- and 7300-series routers into Cisco's new ASR 1000 router, which runs an IOS variant called IOS XE.

FactSet CTO Jeff Young says IOS XE is a "significant change" to IOS that includes additional complexity and cost in learning the nuances of the new operating system; but the benefits outweigh the inconveniences.

IOS XE offers the ability to perform in-service upgrades of hardware and software, whereas the 7200s and 7300s with older versions of IOS had to be taken out of service for those modifications, Young says. But in the end, IOS XE still feels like IOS, he says.

"I guess you could call it learning a new operating system," Young says. "To my network engineering staff, IOS is IOS: You log into the thing, it feels like you're at home. Certainly the mechanics of it are different. But to the network engineer to provision services and do the normal course of business, you haven't changed his life very much."

Cisco says there's a good reason for that.

"Goal No. 1: It must look exactly like IOS," says Doug Gourlay, Cisco senior director of datacentre solutions, explaining the company's strategy when it develops an IOS variant. "If you look at what we’ve done in NX-OS, we took software developed in the IOS group, brought it over - common look-and-feel, common operational characteristics, common code, common command interpreter - and are running that natively on top of a Linux operating system. [Users] probably wouldn't be able to tell the difference. Except for where we've chosen not to implement a particular feature set or type...we've defaulted to putting it in the same way we've already done it before, so it was consistent from a customer perspective."

A Linux operating system kernel allows Cisco and its customers to add IOS services as modules, and facilitates virtualised operation of those services, Gourlay says. IOS traditionally has been a monolithic operating system, where services and operations were tightly linked to the kernel, necessitating a wholesale replacement of the software to access new features, critics say.

Gourlay says the new IOS variants - IOS XR, IOS XE and NX-OS - are designed to support specific applications in different areas of the network. IOS XR was developed for multi-chassis scaling in the core, IOS XE for the different requirements at the edge, and NX-OS for consolidating storage and Ethernet capabilities in the datacentre.

"We've had to apply different architectural approaches to maintaining software segmentation, keeping feature velocity up, being able to trace a defect...to fix it quickly," Gourlay says. Cisco will continue to consolidate its product-specific operating system platforms over the next six to 12 months, he says.

In the end, the significance of a single operating system vs multiple operating systems will be up to the customer. For now, users are taking Juniper's ongoing JUNOS integration work in stride, just as they are taking in stride Cisco's approach to delivering a specific operating system dedicated to a specific networking task.

"The only time a user would get concerned about whether there are multiple operating systems is if it affected the way he dealt with the multiple products," says Current Analysis' Hunt. "There’s probably a certain type of customer out there that would prefer to have one. But I haven't seen where it's really hurt them."