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372 CHAPTER 24: CONFIGURING IPX
network routing information which can be sent to destination or needs to be
forwarded, so that when a packet is received, the next router can be found to
transmit the packet. The routing information here can be configured both
statically and dynamically. In a router, collection and maintenance of dynamic
routing information are realized by RIP.
RIP is an abbreviation for Routing Information Protocol. A router creates and
maintains an inter-network routing information database (usually called router
information table) through RIP. When the router starts, RIP begins exchange of
routing information with external RIPs enabled hosts constantly. When creating a
new path, RIP adds its routing information into the router information table, and
when finding a faulty path, RIP deletes its routing information from the router
information table. It can be seen that the router information table reacts flexibly to
inter-network error and congestion. In case of error and congestion, the router
information table can be modified dynamically to change the path. The following
diagram describes the relation between main components of RIP.
Figure 135 Schematic diagram of the relation between main components of RIP
SAP
SAP is an abbreviation for Service Advertising Protocol. SAP allows providing
various service nodes, such as file server, print server, NetWare access server and
remote control console server, and broadcasting their service types and addresses.
When servers start, they broadcast their services through SAP, and when serves are
shut down, they indicate the termination of services through SAP.
Through SAP, a router creates and maintains an inter-network service information
database, usually called service information table. It tells what services are
provided by the network, and what inter-network addresses these servers have.
This is an important function, for a workstation cannot establish session with file
servers if it does not know their addresses.
A server that provides services will periodically broadcast its services and address to
the adjacent sites. Clients cannot use such information directly, it is collected by
SAP agents in different routers on the network, and saved in their server
information tables. Since server information is often dynamically updated by SAP,
Router
Information Table
Periodic
Broadcast Process
Aging Process
IPX Process
NICs and Drivers
Timer
RIP Process
Timer
Socket
0x453
RIP Request/Response Packets
Routing Information