Modifying DA Advertising and Discovery Frequency

In some situations, you might need to modify the frequency of DA advertising or DA discovery. DA advertising and discovery are controlled by the following properties:

• net.slp.DAHeartBeat - Controls how often a DA multicasts an unsolicited DA advertisement

• net.slp.passiveDADetection - Controls whether slpd listens for unsolicited DA advertisements

• net.slp.DAActiveDiscoveryInterval - Controls how often slpd periodically performs active DA discovery for new DAs

The reasons why you might want to modify the default DA advertising and discovery configuration are:

• If you want all SAs and UAs to obtain their DA configuration information statically rather than through discovery, you can configure the properties to disable DA discovery.

• If your network is subject to frequent partitions, or UA and SA clients are accessing a DA over a dial-up network, you can configure the frequency of passive advertisements and periodic active discovery to either increase or reduce the period.

• If network congestion is high, you might need to limit multicast.

Limiting UAs and SAs to Statically Configured DAs

In some cases, it might be necessary to limit UAs and SAs to obtain only their DA addresses from the static configuration information in the slp.conf file. You can accomplish this by disabling passive and active DA discovery in slpd.

Disable passive discovery by setting the net.slp.passiveDADetection property to False. This causes slpd to ignore unsolicited DA advertisements.

Disable initial and periodic active discovery by setting the net.slp.DAActiveDiscoveryInterval to -1. This causes slpd to refrain from performing initial active DA discovery, and from periodically polling for new DAs.

Perform these configurations only on those hosts executing the UAs and SAs that are restricted to using their static configurations. As a consequence of these configuration actions, slpd obtains DA information only from the net.slp.DAAddresses property in the slp.conf file.

Modifying DA Advertising and Discovery Timing

For certain combinations of network media and the overall network topology, you might need to modify the timing of passive DA advertisements and periodic active discovery requests. This section provides these examples:

• If your network is subject to frequent partitions, and SAs tend to remain in operation for long time intervals, you can increase the frequency of the passive DA advertisement frequency.

• If you have a DA on one side of a dial-up connection and UAs or SAs that use the DA on the other side, you can decrease both the DA heartbeat frequency and the active discovery frequency, to decrease the number of times the dial-up line is activated.

Configuring the DA Heartbeat for Frequent Partitions

SAs are required to register with all DAs that support their scopes. A DA can appear after slpd has performed active discovery. If the DA supports slpd scopes, then slpd registers all advertisements on its host with the DA, in order for the set of service advertisements in the scopes to be consistent.

One way slpd discovers DAs is by the initial unsolicited advertisement a DA sends out when it boots. slpd uses the periodic unsolicited advertisement (the heartbeat) to determine whether a DA is still active, and removes the DAs it uses and offers to UAs if a heartbeat fails to appear.

Finally, when a DA undergoes a controlled shutdown, it transmits a special DA advertisement that informs listening SA services that it will be out of service. slpd also uses this advertisement to remove inactive DAs from the cache.

If your network is subject to frequent partitions and SAs are long-lived, slpd can remove DAs from its cache during the partitions if heartbeat advertisements are not received. By decreasing the heartbeat time, you can decrease the delay before a deactivated DA is restored to the cache after the partition is repaired.

The net.slp.DAHeartBeat property controls how often a DA multicasts an unsolicited DA advertisement. By default, the DA heartbeat period is set to 3 hours (10800 seconds). The following entry decreases the DA heartbeat value to one hour:

net.slp.DAHeartBeat=3600

Configuring DA Discovery for Dial-up Networks

If the UAs or SAs are separated from the DA by a dial-up network, you can configure DA discovery to reduce or eliminate the number of discovery requests and DA advertisements. Dial-up networks usually incur a charge when they are activated, so minimizing extraneous calls can reduce the cost of using the dial-up network.

You can disable DA discovery completely using the method described in "Limiting UAs and SAs to Statically Configured DAs". If DA discovery is completely disabled, the net.slp.DAAddresses property must be set in slp.conf on the hosts executing UAs and SAs so that they access the correct DA.

You can reduce unsolicited DA advertisements and active discovery by increasing the DA heartbeat period and the active discovery period. In the following example, both the active discovery interval and the DA heartbeat are set to about 18 hours. The first line shows the setting for the host executing the DA:

net.slp.DAHeartBeat=65535

On the hosts executing the UAs and SAs, the active discovery interval is configured as:

net.slp.DAActiveDiscoveryInterval=65535

Both property values are measured in seconds.

Network Congestion Is High

If network congestion is high, you might want to limit the amount of multicast. If DAs have not already been deployed in the network, deploying DAs can drastically cut back on the amount of SLP-related multicast.

However, even after DAs are deployed, multicast is still necessary for DA discovery. You can reduce the amount of multicast necessary for DA discovery using the method described in "Configuring DA Discovery for Dial-up Networks". You can completely eliminate multicast for DA discovery using the method described in "Limiting UAs and SAs to Statically Configured DAs".