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Published on Nov 23, 2016
Deploying a Stateful and Fault Tolerant Virtual Gateway Using Open vSwitch in a Sotware Defined WAN- Sabyasachi Sengupta, Alcatel-Lucent
With growing deployment of virtual switches as gateways in a Software Defined WAN (SDWAN) enabled branch, there is ever growing need to improve reliability by making it fault tolerant and highly availabile. One of the popular means of achieving high availability is provisioning redundant gateways that operates as an active-passive pair. In production of enterprise networks of large corporations such as branches of banks, where connectivity between cloud data centers and the branch is critical, a fault tolerant network needs to guarantee minimal traffic loss and maximal state replication of the "authoritative" gateway at the "secondary" gateway in steady state. Modern day virtual networking switches are known to offer additional services such as DHCP server, NAT/PAT support etc. If these states are saved persistently in the authoritative gateway, such state need to be synced continuously to the secondary as seamlessly as the heartbeat exchange of the two gateways. Open vSwitch is often used at the heart of such a Virtual Network in SDWAN and supports various heartbeat exchange mechanisms such as Bidirectional Forwarding Detection (BFD, RFC5880) that detects faults in the forwarding path between two forwarding engines. This paper illustrates an extension to RFC5880 for implementing a notion of mastership role to each access link that is managed by the virtual switch. When one of the links (ports) fail at the authoritative gateway and BFD link fail detection occurs, the secondary gateway automatically takes over the ownership of passing traffic thereby assuming temporary mastership until link is restored. With a stateful synchronization of all the state of the primary gateway, the secondary not only reads the peer state and continues to operate seamlessly with same state as primary, but also performs all the networking services just as the original authoritative gateway would have done. While building networks of scale in a Software Defined Networking paradigm, the mastership configuration can be applied on the gateway through an openflow controller, which can relay the config that is provisioned at openstack director UI.