Configuring the net.slp.interfaces Property

If the net.slp.interfaces property is set, slpd listens for unicast and multicast/broadcast SLP requests on the interfaces listed in the property, rather than on the default interface. For example, suppose a server with three network cards and multicast routing turned off is connected to three subnets. And suppose the three network interfaces have IP addresses 192.147.142.42, 192.147.143.42, and 192.147.144.42 and that the subnet mask is 255.255.255.0. The following property setting causes slpd to listen on all three interfaces for unicast and multicast/broadcast messaging:

net.slp.interfaces=192.147.142.42,192.147.143.42,192.147.144.42

You can set the net.slp.interfaces property to either IP addresses in dotted decimal form, as above, or to resolvable host names.

Usually, you set the net.slp.interfaces property in conjunction with enabling broadcast by setting the net.slp.isBroadcastOnly property, because multicast has not been deployed in the network. However, if multicast has been deployed, but is not being routed on this particular multihomed host, it is possible for a multicast request to arrive at slpd from more than one interface. This can happen because another multihomed host or router connecting the subnets served by the interfaces routes the packets.

When this happens, the SA server or UA sending the request gets two responses from slpd on the multihomed host. These responses are filtered out by the client libraries, so the client should not see them. They are visible on the snoop trace, however.

Be careful when configuring the net.slp.interfaces property if unicast routing is turned off. Without unicast routing, any services advertised by SA clients on the multihomed host might not be reachable from all the subnets, unless the SA clients do the following:

• Advertise one service URL for each individual subnet

• Assure that requests from a particular subnet are answered with a reachable URL

The SA client library makes no effort to assure that reachable URLs are advertised. Therefore, it is up to the service program, which might or might not handle a multihomed host with no routing, to assure that reachable URLs are advertised.

Before deploying a service on a multihomed host with unicast routing disabled, you should use snoop to determine whether the service handles requests from multiple subnets correctly. Furthermore, if you are planning on deploying a DA on the multihomed host, see "DA Placement and Scope Name Assignment".