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SDN proponents have focused on OpenFlow as the protocol for decoupling the control plane and data plane of the network, but some vendors are claiming that the southbound protocol you use to get to SDN is less important than the operational agility and programmability that SDN architecture offers -- with or without OpenFlow. These vendors have identified BGP as a potential SDN protocol that can enable the network programmability promised by SDN.
How exactly is BGP being used? The controller uses BGP as "a control plane protocol and leverages NETCONF as a management plane protocol to interact with physical routers, switches and networking services like firewalls," said Ankur Singla, Juniper Network's vice president of SDN and orchestration systems.
This approach "enables SDN to exist in a multi-vendor environment without requiring infrastructure upgrades. OpenFlow doesn't address the issue of the controller interoperability or solve the configuration, so Juniper is advocating for a standards-based approach," Singla said.
Can a controller use BGP to as an SDN protocol to program flows? "The controller operates on multiple levels of abstraction -- from routing and bridging topologies to flow based. BGP doesn't program flows, but operates at a higher level of state like physical and virtual topologies (L2 and L3), security policies, etc.," Singla explained.
While service providers are completely comfortable with BGP, "some data center folks might be less comfortable with it," noted Brad Casemore, research director of datacenter networks for IDC. "Data center folks are concerned about convergence times and view BGP as a WAN protocol rather than one to use inside your data center."
But some vendors are planning to use BGP, as well as other mature protocols, for SDN. Juniper is embracing BGP in its Contrail SDN system and relying on it for network virtualization.
"One of the biggest issues surrounding SDN systems is interoperability of the controllers -- something no one is discussing because it's still early days and everyone wants to run at full speed without being hampered by the standards bodies," said Singla. "But OpenFlow doesn't address this issue of controller interoperability."
That's why Juniper is proposing an architecture that was adopted by the L3VPN Working Group within the Internet Engineering Task Force (IETF) last year -- with the intent to continue to innovate its SDN platform, while working with standards bodies on interoperability standardization.
BGP for SDN can offer capital expense savings by allowing network operators to "seamlessly integrate existing networks and deployed infrastructure components," Singla said. "Also, the reuse of existing protocols prevents the need for lower-performance software gateways to bridge the physical and virtual worlds."
Using BGP and other established protocols can simplify operations, too, by "reducing network complexity and integrating SDN systems with their existing business logic and processes built around years of experience with BGP, MPLS, etc.," Singla said.
Architectural rightsizing is all about using mature technologies known to scale and solve difficult customer problems. "For example, routing has been done for decades without using flows because it scales better. But many L4-L7 services are best done using flows," Singla said.
While traditional protocols are necessary for interoperability with legacy systems and certainly the Internet, in the case of BGP, the question the industry needs to answer is: Do you really want to carry these traditional protocols over into SDN? "It's a big question that's still unresolved," Casemore said. "There's a dichotomy: the cloud doesn't look like the enterprise. The large cloud shops are doing things in a much different way than standard enterprises. There isn't a one-size-fits-all solution at this point."
Click here to learn more about XMPP as an SDN protocol.