SAP Packet Structure
The SAP header, shown in Figure 5.14, immediately follows the IPX header. SAP packets have an IPX Packet Type of 0x04 or 0x00 and Source and Destination Socket numbers of 0x0452.
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Figure 5.14 SAP for IPX Packet Structure
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Note
Figure 5.14 depicts the packet structure for the SAP Response and SAP GetNearestServer Response. The SAP Request and SAP GetNearestServer Requests packets only contain the Operation and Service Type fields and are 34-byte packets (30 bytes for the IPX header, 4 bytes for the SAP header).
Operation The 2-byte Operation field indicates the type of SAP message. Table 5.3 defines the values for the Operation field.
Table 5.3 SAP Operations
Operation |
Type of Message |
Description |
|---|---|---|
1 |
Request |
Sent by a router or SAP client to request all services or all services of a specified type. |
2 |
Response |
A reply to a SAP Request. Periodic SAP advertisements are also sent as a SAP Response. |
3 |
GetNearestServer Request |
Sent by a workstation to request the IPX internetwork address of the nearest (quickest response) server of a specified service type. |
4 |
GetNearestServer Response |
Sent in response to the SAP GetNearestServer Request and contains a single name and IPX internetwork address of the nearest server of a requested service type. |
Following the Operation field is a series of up to seven SAP services in the same SAP message for a maximum SAP packet size of 480 bytes. If more than seven services need to be sent, they are sent in multiple SAP packets.
Service Type The 2-byte Service Type field indicates the type of service that the service provides. Service types are assigned uniquely by Novell, Inc. Some commonly defined SAP service types are listed in Table 5.4. For a complete list of SAP service types, see the SAP link at https://windows.microsoft.com/windows2000/reskit/webresources .
Table 5.4 SAP Service Types
Server |
Service Type (hexadecimal) |
|---|---|
Unknown |
00-00 |
NetWare File Server |
00-04 |
NetWare Print Server |
00-07 |
Microsoft RPC Server |
06-40 |
General SAP Request |
FF-FF |
Server Name The 48-byte Server Name field stores the name of the server advertising the service. The combination of Server Name and Service Type uniquely identifies a service on an IPX internetwork. Server names under 48 bytes are terminated with the ASCII NULL character.
Network Number The 4-byte Network Number field indicates the IPX network number where the server hosting the service resides.
Node Number The 6-byte Node Number field indicates the IPX node number where the server hosting the service resides.
Socket Number The 2-byte Socket Number field indicates the socket number on which the service process is listening.
Intermediate Networks The 2-byte Intermediate Networks field indicates the number of routers to traverse to reach the server hosting the service.