SLP on NetWare 5.1 - Page 2

By Drew Bird | Posted Feb 22, 2001
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Having DAs on the network affects how SAs function. If an SA discovers a DA, it immediately sends all of its registered services directly to the DA. SAs can discover whether a DA exists through a process called active discovery. To perform active discovery, SAs send multicast transmissions to the IP address 224.0.1.35. Servers acting as DAs respond to these discovery packets and initiate the registration of services.

UAs also have the ability to automatically recognize the existence of a DA, providing the ability for network administrators to make a DA-centered environment with minimal configuration. Any NetWare 5.x server can act as a DA by loading SLPDA.NLM.

An alternative to the active discovery process is to manually configure the SAs and UAs with the address of the DA. For servers, this configuration information can be provided through the use of a text file called SLP.CFG or via Dynamic Host Configuration Protocol (DHCP). Likewise, for workstations, the location of the DA can be supplied manually through the Novell client properties, or automatically through the use of DHCP.

No matter how the presence of the DA is detected, one rule remains: If SAs and UAs know that a DA exists on the network, both agents have to use the DA for service registration and resolution.

Scope This Out

If you crave even more control of your SLP-related traffic, SLP also provides the ability to use scopes to group network resources into logical units. By creating scopes on your network, traffic can be even more controlled, because agents will only communicate with other agents (be they SA, UA, or DA) that are in the same scope as themselves.

SLP and NDS
When DAs are used, SLP objects and records are stored in the NDS. This process allows SLP-related information to be replicated between servers as part of the standard NDS replication process.

For example, imagine that you have a Wide Area Network (WAN) with two sites. By creating a scope for each site, you can prevent SLP traffic from being propagated across the wide area link. All of the resources on site A are configured to be within Scope A, and all the resources on site B in Scope B. To make sure that resources in another scope are still available to the whole network, you can either take advantage of Novell Directory Services (NDS) partitioning and replication or manually configure DAs with the information necessary to exchange data with other DAs. Another, less practical, solution is to configure each client PC with the IP address of DAs on both sites.

By now, you may well be asking yourself whether you should create DAs and configure a custom SLP environment on your NetWare network. Well, according to Novell, you should use DAs if your network includes more than 25 NetWare servers, or if you have a WAN. In reality, the amount of configuration required means that implementing DAs is a simple task. If you are looking for ways to streamline the traffic on your NetWare network, using DAs is a simple way of reducing unnecessary network traffic. //

Drew Bird (MCT, MCNI) is a freelance instructor and technical writer. He has been working in the IT industry for 12 years and currently lives in Kelowna, BC., Canada. You can e-mail Drew at drew.bird@tecmetrix.com.

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