Telco data center operators have recently begun to consider how to bring the benefits of virtualisation to the networking domain. OpenStack has been rapidly gaining traction, but concerns remain that it lacks some of the functionality required to support highly available and highly scalable networks. Numerous vendors have taken up the challenge of filling that gap.
Overlays are emerging as one way to provide the connectivity needed to support the networking needs within the data center. Overlays abstract the details of the physical network, making it much faster to connect virtual machines (VMs) and other devices. Rather than provision paths on physical devices, overlays encapsulate traffic using protocols such as VXLAN and NVGRE to tunnel across the physical network. These newer protocols allow operators to move beyond the limitations of VLANs, which only support 4,096 virtual networks, so they can better support multi-tenant cloud services.
Network functions virtualisation (NFV) is another big factor in the overlay movement. In NFV, functions that had previously resided on purpose-built, proprietary platforms will be supported on general-purpose (a.k.a. white-box) servers in the form of virtualised network functions (VNFs). How these workloads will behave in terms of elasticity and mobility is still to be determined, but overlays are seen as an effective approach to providing the flexibility needed to manage VNFs. Overlay networks also make it easier to move workloads between and across data centers. By mapping VXLAN to MPLS paths, virtual private networks can be extended beyond the data center across the WAN.
But the overlay approach does have some potential drawbacks. For one, overlays can potentially introduce more complexity into the data center environment. Opinions vary as to how significant this issue is: Some argue that in the end, operational expense will decline, because less time will be spent managing the physical network; others contend that managing service performance will become more complicated from having two domains to consider. Even when overlays are present, the physical network will remain critical for ensuring service quality.
In talking to network operators, I’m hearing some early overlay optimism that the benefits will ultimately outweigh these concerns. No doubt it will take time for telcos to get comfortable with the new approach. But at this point, with competitive pressures coming as much from outside the network operator realm (think Google, Amazon, and the like) as from within, telcos no longer have the luxury of setting a leisurely pace for data center innovation.
Written by: Roz Roseboro, senior analyst, Heavy Reading
