The Elements of IPX Routing 5-11
Workstations cannot initiate a session with a file server without first knowing
the server’s address.
SAP Packet Structure
SAP uses IPX and the medium-access protocols for its transport. The packet
structure allows for the following functions:
■A workstation request for the name and address of the nearest server of a
certain type
■A router request for the names and addresses of either all the servers or all
the servers of a certain type on the internetwork
■A response to either a workstation or router request
■Periodic broadcasts by servers and routers
■Changed server information broadcasts
Figure 5-5 provides an overview of the SAP packet structure. Notice that the
packet structure is encapsulated within the data area of IPX.
Figure 5-5 SAP Packet Structure
A SAP packet consists of the following fields:
■Operation — This field indicates the type of operation the SAP packet
performs and can be set to one of the following values:
1=Request
2=Response
3=Get Nearest Server Request
SAP Packet Structure
Operation (2 Bytes)
Server Entry (1) (64 Bytes)
Server Entry (n) (64 Bytes)
(n <= 7)
.
.
.
.
Packet Type = 4
Socket =452h
IPX Packet Format
IPX Header (30 Bytes)
Data
Server Entry Structure
Service Type (2 Bytes)
Server Name (48 Bytes)
Network Address (4 Bytes)
Node Address (6 Bytes)
Socket Address (2 Bytes)
Hops to Server (2 Bytes)