Attendre: Mitigating Ⅲ Effects of Race Conditions in OpenFlow via Queueing Mechanism

摘要

According to the specification of the OpenFlow protocol, whenever a flow table entry is absent for any arriving data packet, a packet-in message is sent to the controller. This behaviour results in various types of race conditions in accord with various packet and message orderings. Increased forwarding delay of data packets, increased complexity in performing software verification, and increased load on switch and controller processors are the ill effects of these races. We identify three types of races inherent in the OpenFlow protocol. The Type 1 race is between data packets sent by a host and the command messages sent by the controller. Consider the scenario in which a host has sent two data packets sequentially. The switch, on receiving the first data packet, finds out that there is no entry matching the packet header, so according to the default action, a packet-in message is sent to the controller. The controller processes this packet-in message and sends out a flow-mod message combined with a packet-out message (denoted by flow-mod/packet-out) to the switch.