Configuring a LAN/WAN infrastructure for SLP

  • 10014467
  • 4.0.25972966.2280499
  • 17-Aug-1999
  • 08-Jul-2005

Archived Content: This information is no longer maintained and is provided 'as is' for your convenience.


Configuring a LAN/WAN infrastructure for SLP


Formerly KB 2951566


This is one document in a series of documents that are designed is to provide network administrators with the settings and other configuration parameters associated with Service Location Protocol (SLP) and the configuration of User Agents, Server Agents, and Directory Agents. This document will be periodically updated as new information becomes available or settings change in newer versions. Other related documents include:

TID 10025313 - Frequently Asked Questions about SLP
TID 10014396 - "SLP Terms and Configuration Reference"
TID 10014467 - "Configuring a LAN/WAN infrastructure for SLP"
Configuring SLP for a NetWare Client
TID 10027163 - "Configuring SLP for a NetWare Server
TID 10062474 - "SLP Design and Implementation Guidelines"


There are several infrastructure conditions that make the configuration of a DA (Directory Agent) strongly desireable. These conditions include:

1. If there is any type of slow link between sites (less than 10 Mbps).

2. If a UA must communicate with an SA across 2 or more routers (multicasting must be enabled).

3. If you have over 25 servers within the same multicast radius.

4. If you have UA's and SA's that must communicate accros a WAN link and Multicasting is NOT enabled you MUST configure DA's

If any of these conditions exist, Novell STRONGLY recommends doing the following:

1. Prevent multicasting across WAN links by disabling Multicasting on routers for the port that goes to a WAN link. SLP communication will be unicast across the WAN with the proper DA configuration. See the MULTICAST ADDRESSES USED BY SLP section below for what Multicast addresses SLP uses.

2. Configure at least one (1) DA in your network at a central location.  Do not configure more than two to four DA's to service a scope.  If you have a large network you will want to configure multiple scopes.  Have each DA for other scopes register as an SA with the central scope by editing the ETC\SLP.CFG file to point to the central DA.  

3. If using multiple DA's across WAN links, configure the DAs with a replica of the NDS partition containing the Scope Unit on each server (will update SLP Service register/deregisters by NDS object replication).

4. Determine if you want the SAs to use Static, DHCP, or Dynamic discovery of DAs.

    1. Configure the SYS:\ETC\SLP.CFG for each site.  Each NetWare 5 server will come with a sample SLP.CFG file.  This will need to include the IP Address of each DA that this server is to register its services with and obtain service information from. (do not include those across a WAN link unless absolutely necessary).

    2. Ensure that the SET SLP DA DISCOVERY OPTIONS has the binary 4 bit enabled. See KB 2951564 for information about how to set this parameter.

    3. You will have to either restart the server or unload/reload SLPTCP.NLM and SLP.NLM for the new settings to take effect.

    1. Configure the Scope and DA list on the DHCP server. See the "Dynamic Host Configuration Protocol (DHCP)" section of KB 2951567 for information on the DHCP options and current limitations on SAs receiving DA configuration information from DHCP.

    2. Ensure that the SET SLP DA DISCOVERY OPTIONS has the binary 2 bit enabled. See KB 2951564 for information about how to set this parameter.


    1. Ensure that the SET SLP DA DISCOVERY OPTIONS has the binary 1 bit enabled. See KB 2951564 for information about how to set this parameter.

    2. Ensure that multicasting is enabled on routers between any SA and the DA they should be registering their SLP services with. See the "MULTICAST ADDRESSES USED BY SLP" below for what multicast addresses SLP uses.

NOTE: It is possible to use a combination of 2 of these options or even all 3. In the event that DAs have been discovered using multiple methods, the precedence for which is used for queries is Static, DHCP, and then Dynamic. The SA will still register to all Active DAs, no matter what method was used to discover them.

5. Ensure that the TCP/UDP ports used by SLP on all routers are enabled where SLP Requests need to cross. This includes both Unicast and Multicast requests, so even if you disable Multicast on a router, you should still ensure that the appropriate TCP/UDP port are enabled to allow SLP Unicast packets to travel between sites. See the IP PORTS USED BY SLP section below for what TCP/UDP ports are used by SLP.

In general, not configuring a DA reduces the efficiency of the SLP technology. When a DA is not present, then each UA must attempt to locate SLP services via multicast and this multicast packet must be able to reach the SA who has registered the desired SLP Service (SAs do not exchange SLP Service information at all, each SA only tracks it's own SLP Services).


1. Determine the MTU (Maximum Transmission Unit) that your infrastructure supports. The SLP services running on a NetWare Server will support an MTU of up to 24682 bytes, while the SLP services running on a Novell Client will support an MTU of up to 4096 bytes. The defaults for this setting are 1450 and 1400 bytes respectively. The larger the negotiated MTU between the Server and Client, the fewer the packets that will be required for certain types of SLP query responses (where the SLP DA/SA is giving a list of requested services that with the default MTU settings would have had to have been split into multiple response packets). These SLP query responses will use a larger packet, but will overall be more efficient since less packet space is used for the IP header and also routers are more efficient in routing a single large packet than it's equivalent in multiple smaller packets. The following types of hardware will affect what your infrastructure MTU is:
1. Routers
2. Switches
3. Bridges
4. Network Interface Cards (NICs)
5. non-passive hubs (any device that must buffer a packet before forwarding it on)

Contact the vendor of the specific hardware to find out what the maximum MTU they support is.

MULTICAST ADDRESSES USED BY SLP: - DA Service Query or DAAdvert. The Service Query is typically used by a UA or SA to dynamically discover DAs. The DA Advertisement is used when a DA first loads to advertise itself to SAs with Active Discovery enabled. The DA Advertisement is also used by the DA Heartbeat to periodically advertise itself on the network using multicast. - SA General Service Query. The General Service Query is typically used by a UA to locate an SA when when a DA is not locatable (no static or DHCP configuration and no DA responds to the DA Service Query) or is disabled on the Client.


427 - SLP
524 - NCP
2302 - SCMD
2645 - SCMD

427 - SLP
524 - NCP
2302 - SCMD
2645 - SCMD.