Discovery configuration

Discovery addresses

The DDSI discovery protocols:

  • Simple Participant Discovery Protocol (SPDP) for the domain participants (usually operates well without any explicit configuration).

  • Simple Endpoint Discovery Protocol (SEDP) for their endpoints (never requires configuration, see Endpoint discovery).

For each domain participant, the SPDP protocol periodically sends an SPDP sample to a set of addresses (the default only contains the multicast address):

  • IPv4 (

  • IPv6 (ff02::ffff:

To override the address, set the: Discovery/SPDPMulticastAddress (requires a valid multicast address).

In addition (or as an alternative) to the multicast-based discovery, any number of unicast addresses can be configured as ‘addresses to be contacted’, by specifying peers in: Discovery/Peers. Each time an SPDP message is sent, it is sent to all of these addresses.

The default behaviour is to include each IP address several times in the set of addresses (for participant indices 0 through Discovery/MaxAutoParticipantIndex). Each IP address then has a different UDP port number, each corresponding to a participant index. Configuring several peers in this way causes a large burst of packets to be sent each time an SPDP message is sent out, and each local DDSI participant causes a burst of its own messages. Because most participant indices are not used, this is wasteful behaviour and is only attractive when it is known that there is a single DDSI process on that node.

To avoid sending large numbers of packets to each host (that differ only in port number), add the port number to the IP address (formatted as IP:PORT). This requires manually calculating the port number.

To ensure that the configured port number corresponds to the port number that the remote DDSI implementation is listening on, also edit the participant index by setting: Discovery/ParticipantIndex (see the description of “PI” in Port numbers).

Asymmetrical discovery

On receipt of an SPDP packet, the addresses in the packet are added to the set of addresses to which SPDP packets are periodically sent. For example:

If SPDP multicasting is disabled entirely:

  • Host A has the address of host B in its peer list.

  • Host B has an empty peer list.

B eventually discovers A because of an SPDP message sent by A, at which point it adds A’s address to its own set and starts sending its SPDP message to A, therefore allowing A to discover B. This takes longer than normal multicast based discovery, and risks Writers being blocked by unresponsive Readers.

Timing of SPDP packets

To configure the interval with which the SPDP packets are transmitted, set Discovery/SPDPInterval.


A longer interval reduces the network load, but also increases the time discovery takes (especially in the face of temporary network disconnections).

Endpoint discovery

Although the SEDP protocol never requires any configuration, network partitioning does interact with it.

To completely ignore specific DCPS topics and partition combinations, set the Partitioning/IgnoredPartitions. This option prevents data for these topic/partition combinations from being forwarded to and from the network.