Mininet OpenvSwitch Multi-controller Configuration

Question

According to OpenFlow specification, OpenFlow switch can be connected to multiple controllers with different role.

I am now implementing mininet topology with OpenvSwitch. I would like to know how to specify the role of controllers to OpenvSwitch in Mininet?

Answer 1

The role is determined by the controller, please see the A 3.9. section in the Openflow 1.3 specification:

A.3.9 Role Request Message When the controller wants to change its role, it uses the OFPT_ROLE_REQUEST message with the following structure:

OpenFlow Switch Specification Version 1.3.0
/* Role request and reply message. */
struct ofp_role_request {
    struct ofp_header header; /* Type OFPT_ROLE_REQUEST/OFPT_ROLE_REPLY. */
    uint32_t role; /* One of NX_ROLE_*. */
    uint8_t pad[4]; /* Align to 64 bits. */
    uint64_t generation_id; /* Master Election Generation Id */
};
OFP_ASSERT(sizeof(struct ofp_role_request) == 24);

The field role is the new role that the controller wants to assume, and can have the following values:

/* Controller roles. */
enum ofp_controller_role {
    OFPCR_ROLE_NOCHANGE = 0, /* Don’t change current role. */
    OFPCR_ROLE_EQUAL = 1, /* Default role, full access. */
    OFPCR_ROLE_MASTER = 2, /* Full access, at most one master. */
    OFPCR_ROLE_SLAVE = 3, /* Read-only access. */
};

If the role value is OFPCR_ROLE_MASTER, all other controllers which role was OFPCR_ROLE_MASTER are changed to OFPCR_ROLE_SLAVE. If the role value is OFPCR_ROLE_NOCHANGE, the current role of the controller is not changed ; this enable a controller to query its current role without changing it.

Upon receipt of a OFPT_ROLE_REQUEST message, the switch must return a OFPT_ROLE_REPLY message. The structure of this message is exactly the same as the OFPT_ROLE_REQUEST message, and the field role is the current role of the controller.

Additionally, if the role value in the message is OFPCR_ROLE_MASTER or OFPCR_ROLE_SLAVE, the switch must validate generation_id to check for stale messages. If the validation fails, the switch must discard the role request and return an error message with type OFPET_ROLE_REQUEST_FAILED and code OFPRRFC_STALE.