3.4.5 Processing Events and Sequencing Rules

A Replication Partner AutoDiscovery message with an OpCode of 0 is sent to the multicast group at the service startup time and also periodically while the NBNS server is running. It announces that the NBNS server is up and operational. The NBNS server also sends a Replication Partner AutoDiscovery message with OpCode 1 to the multicast group just before the service stops. A Replication Partner AutoDiscovery message contains all the IPv4 addresses of the server's NIC to which the NBNS service is bound. The NBNS server SHOULD add an 0.0.0.0 address to the end of the list of addresses.

When an NBNS server receives a Replication Partner AutoDiscovery message, it checks whether it is configured to discover partners. If not, the packet is discarded. After validation of the message, the NBNS server extracts all the IPv4 addresses in the message. If an address is 0.0.0.0, this address and all the addresses after it are ignored. If the OpCode field is 0, then all the IPv4 addresses are added as both pull and push partners. These partners are called self-discovered partners. If the OpCode field is not 0, then any self-discovered partner with an IPv4 address in the message is no longer considered as a replication partner.