Thursday, September 11, 2014

HP proposes hybrid OpenFlow discussion at Open Daylight design forum

Hewlett-Packard, an Open Daylight platinum member, is proposing a discussion of integrated hybrid OpenFlow at the upcoming Open Daylight Developer Design Forum, September 29 - 30, 2014, Santa Clara.

Topics for ODL Design Summit from HP contains the following proposal, making the case for integrated hybrid OpenFlow:
We would like to share our experiences with Customer SDN deployments that require OpenFlow hybrid mode. Why it matters, implementation considerations, and how to achieve better support for it in ODL

OpenFlow-compliant switches come in two types: OpenFlow-only, and OpenFlow-hybrid. OpenFlow-only switches support only OpenFlow operation, in those switches all packets are processed by the OpenFlow pipeline, and cannot be processed otherwise. OpenFlow-hybrid switches support both OpenFlow operation and normal Ethernet switching operation, i.e. traditional L2 Ethernet switching, VLAN isolation, L3 routing (IPv4 routing, IPv6 routing...), ACL and QoS processing

The rationale for supporting hybrid mode is twofold:
  1. Controlled switches have decades of embedded traditional networking logic. The controller does not add value to a solution if it replicates traditional forwarding logic. One alternative controller responsibility is that provides forwarding decisions when it wants to override the traditional data-plane forwarding decision.
  2. Controllers can be gradually incorporated into a traditional network. The common approach to enterprise SDN assumes a 100% pure SDN-controlled solution from the ground-up. This approach is expensive in terms of actual cost of new switches and in terms of downtime of the network. By providing a controller that can gradually migrate to an SDN solution, the hybrid approach enables customers to start seeing the value of having an SDN controller without requiring them to make a huge leap in replacing their existing network.
The Open Networking Foundation (ONF), the body behind the OpenFlow standard, released Outcomes of the Hybrid Working Group in March 2013, concluding:
On the whole, the group determined that industry can address many of the issues related to the hybrid switch. ONF does not plan or intend to incorporate details of legacy protocols in OpenFlow. The priority of ONF in this context is to explore the migration of networks to OpenFlow.
OpenDaylight has broad industry participation and should be a good forum to discuss integrated hybrid OpenFlow use cases, enhance open source controller support, and address multi-vendor interoperability. HP should find support for integrated hybrid OpenFlow among Open Daylight members:
SDN fabric controller for commodity data center switches discusses a number of use cases where an SDN controller can leverage the hardware capabilities of commodity switches through industry standard sFlow and hybrid OpenFlow protocols.

Integrated hybrid OpenFlow is a practical method for rapidly creating and deploying compelling SDN solutions at scale in production networks. It's encouraging to see HP engaging the Open Daylight community to deliver solutions based on hybrid OpenFlow - hopefully their proposal will find the broad support it deserves and accelerate market adoption of hybrid OpenFlow based SDN.
Update October 8, 2014: Slides from the summit are available, OpenFlow-hybrid Mode


  1. The hybrid approach looks very appealing but how do you setup the traditional protocols on the switch? you would still need to do switch by switch configuration for those protocols. Maybe we need a solution to automate the basic network setup then use Openflow to stir traffic.


    With integrated hybrid mode can you have a flow that modifies a packet then send to normal action?

  2. The NORMAL action is an important feature for addressing hybrid OpenFlow use cases - Super NORMAL. You are correct, you still need to automate the basic network setup. The ONF standardized the OF-Config protocol (built on NETCONF) to bring up OpenFlow networks. You could use NETCONF to bring up switching and routing protocols in a hybrid OpenFlow network (NETCONF is one of the southbound protocols in OpenDaylight).

    The essential requirement is that the platform provide a way of composing normal forwarding with selective overrides. The hybrid approach to SDN isn't limited to OpenFlow. Hybrid SDN controllers can be built around I2RS, BGP FlowSpec, or implemented directly on open networking platforms like Cumulus Linux (RESTful control of Cumulus Linux ACLs).

    Cumulus Linux demonstrates a different approach to automating configuration management. Instead of relying on NETCONF, you can use tools from the DevOps space to manage switch and server configurations, e.g. Puppet, Chef, Ansible, CFEngine, etc.

  3. One practical application for this is to use the Hybrid switch to peer with a traditional core router for routing between OF and legacy networks. Could one install a static flow in the regular routing table with OF then have that route propagated upstream?

    Do you have a packet walk through example for normal action? can you modify the packet then output to normal?

    1. OpenFlow rules are applied to the FIB and aren't visible to the routing protocol. Hybrid OpenFlow could be extended to operations on the RIB, but currently SDN efforts in the routing space are targeted at protocols like I2RS or BGP.