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Johnson replaces Scott Kriens, who had led the company for 12 years and will continue as chairman of Juniper's board.

Johnson was president of Microsoft's Platforms and Services Division, its largest business unit, and was part of the team that spearheaded the software maker's failed pursuit of Yahoo.

Microsoft announced Johnson's departure on Wednesday, alongside a reorganisation that split the division into two: one focused on the dominant Windows operating system and the other focused on its lagging online business.

Juniper makes most of its revenue from selling high-performance routers to communications service providers. Earlier this year, it expanded into the market for ethernet switches, which direct traffic on corporate data networks, moving into more direct competition with bigger rival Cisco Systems.