HP HPE VAN SDN Controller 2.7 Administrator's Manual page 130

Initially, the REST API reports only one link; the link between the Comware 5500Hl and the
ProVision 3800:
The Rest API reports the link discovered when the controller injected link discovery packets to
the ProVision 3800 OpenFlow instance. The ProVision switches insert a VLAN tag in packets
injected by the controller when the egress ports are configured as tagged only. The 5500 port
receives the properly tagged packet and forwards it to the controller, resulting in the discovered
link.
The corresponding link from the 3800 to the 5500 is missing. The controller-injected link discovery
packets sent to port GigabitEthernet/1/0/14 on 5500 OpenFlow instance (the device with DPID
00:01:cc:3e:5f:6a:d3:80) were not tagged, therefore they were dropped by the receiving 3800
whose port 6 is configured for tagged traffic.
Solution
To ensure link discovery packets are tagged when sent out by tagged Comware device ports,
configure the device linkDiscoverVlan value for the Comware device with the tagged-only
port using the device REST API. For example, in the above topology, configure the 5500 device
to set the linkDiscoveryVLAN to 40 (the VLAN configured in the OpenFlow instances):
130 Configuring OpenFlow instances