Home » HP » HP2-Z31 » Which protocol is used by the OpenFlow switches to discover this multi-hop link?
Two HP OpenFlow switches are connected to an intermediate layer 2 switch running LLDP, but not OpenFlow. This intermediate switch is configured with a single VLAN. Which protocol is used by the OpenFlow switches to discover this multi-hop link?
A. CDP
B. ND
C. LLDP
D. BDDP
Correct Answer: D
Explanation/Reference:
Explanation: The LLDP messages allow the link service to discover that there is physical link between two switches. If the LLDP message on one side of the link (Packet_Out) is received on the other side of the link (Packet_In) by a switch, LS knows that the two switches are connected to each other.
The service is also responsible for identifying multi-hop links. These are links where non- OpenFlow devices are connected between two OpenFlow switches and thus separate the OpenFlow switches. The Link Service does this by sending BDDP (Broadcast version of LLDP) messages in addition to LLDP messages. LLDP is a one hop protocol and may be consumed by a non-OpenFlow switch because LLDP uses a multicast address which the intermediate switch may have subscribed to the LLDP multicast. However, a broadcast frame (BDDP) will be forwarded typically by the intermediate switch. BDDP has the same TLV information as LLDP.
Reference: HP SDN Network Services Modules
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