Service advertising

Servers on a NetWare network advertise their services and IPX addresses with the Service Advertising Protocol (SAP). The information that these servers broadcast is not used directly by clients but, instead, is collected by a SAP agent within each NetWare router on the server's segment. The SAP agents store this information in a Server information table and, if they reside within a server, in their server's bindery. The clients can then contact the nearest SAP agent or file server for server information.

The SAP broadcasts that servers perform are local broadcasts and, therefore, only received by SAP agents on their connected segments. Consequently, SAP agents periodically broadcast their server information so that all SAP agents on the network have information about all servers that are active on the network -- this is the same broadcast method used by routers to distribute and exchange network number (RIP) information.

Server information table

The table that SAP agents use to store information received in SAP broadcasts is called the server information table. If all SAP agents on the network are exchanging SAP information properly, each agent's server information table should have information about all the servers on the network, thus providing clients with nearby access to the IPX addresses of all the servers on the network.

The server information table contains the following fields:

Server Name

The name of the server.

Server Address

The service's full IPX address, including the network, node, and socket numbers.

Server Type

A number designating what type of service the server provides. One server might provide printing services as opposed to file services, for instance. The server type designation used to assign numbers to the different services that servers provide is part of a more generic scheme used in the bindery to classify objects. ``Novell object types'' lists some of the more common object types.

Hops to Server

Specifies the number of routers to reach the server.

Time Since Changed

The timer used for aging servers that have unexpectedly gone down.

NIC Number

The number of the NIC on which the information about the server was received.

Novell object types

Services on a network are identified using Novell object types. ``Novell object types'' lists some of the Novell common object types.

Novell object types

Description	Object type (hexadecimal)
User	1
User group	2
Print queue	3
File server	4
Job server	5
Gateway	6
Print server	7
Archive queue	8
Archive server	9
Job queue	A
Administration	B
NAS SNA gateway	21
NACS	23
Remote bridge server	24
Bridge server	26
TCP/IP gateway	27
Gateway	29
Time synchronization server	2D
Archive server SAP	2E
Advertising print server	47
BTrieve VAP 5.0	48
SQL VAP	4C
Xtree network version	4D
BTrieve VAP 4.11	50
Print queue user	53
WANcopy utility	72
TES - NetWare for VMS	7A
NetWare access server	98
NVT server	9E
NetWare 386	107
Communications executive	130
NNS domain	133
NetWare 386 print queue	137
Wildcard	FFFF

Server information administration

When a file server or, in the case of SCO IPX/SPX, SAPD is first brought up, its internal SAP agent:

1. Places the name of the server in the agent's server information table.

2. Sends a SAP broadcast to each of its directly connected segments to inform the SAP agents on those segments that a new server has become available.

3. Broadcasts a request to each of its directly connected segments for information about other servers that exist on the network. These requests are responded to by all the SAP agents on these directly connected segments.

4. Places the information received in these responses in its server information table.

5. Performs broadcasts about the servers that it is aware of every 60 seconds (except on asynchronous and X.25 links).

Sequence used to build and maintain the server information table

As with routing information broadcasts, all server information broadcasts are local broadcasts and are subject to the best information algorithm. Any changes in server information are passed on immediately to ensure current information across the network. The router applies the aging process to its server information table entries in case any servers become unavailable. Finally, if the router is brought down, it will indicate to its directly connected segments that the servers the router has been advertising will no longer be available.

File server addressing

Value-added servers, such as database and print servers, normally contain only one network adapter and use the address of that adapter as the address they advertise in their periodic SAP broadcasts. In contrast, NetWare file servers may contain multiple adapters. This requires that they use some sort of convention for advertising the address of their file services; the convention used for this addressing differs for 286- and 386-based servers.

Within the 286-based environment, the services of a file server are addressed with respect to its first NIC, A. This convention guarantees consistency because every server will have at least one network adapter installed. ``Addressing of file services on a 286-based NetWare file server'' illustrates this convention.

Addressing of file services on a 286-based NetWare file server

In the NetWare 386-based servers, an internal network has been added for the addressing of internal services, as shown in ``Addressing of file services on a 386-based NetWare file server''. This different method of addressing requires that an internal network number be assigned when a NetWare 386-based file server is brought up. SCO IPX/SPX requires an internal network number.

Addressing of file services on a 386-based NetWare file server

NetWare 386-based servers can be distinguished by a node number of one. This node number is assigned to the file services on the internal network number.