3Com MSR 50 Series, Руководство по настройке

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2218 C
HAPTER
128: IPX C
ONFIGURATION
Via RIP, an IPX router exchanges routing information with neighbors and maintains
an inter-network routing information database (usually called routing table)
according to network changes. When the router receives a packet, it finds a next
hop from the routing table to forward the packet.
IPX SAP Service advertising protocol (SAP) is used to advertise the service types that servers
provide and their addresses. IPX advertises dynamic service information through
SAP. When a server starts, it broadcasts services it can provide through SAP. When
being shut down, the server informs clients of the termination of services through
SAP.
Through SAP, an IPX router creates and maintains an inter-network service
information database (usually called service information table). A server on the
same network periodically broadcasts its service types and address. Clients not on
the same network as the server cannot get such information directly which is
collected by the SAP proxy and saved in the server information table in the IPX
router for advertisement to such clients. Since server information is dynamically
updated by SAP, clients can always obtain latest server information.
SAP defines three types of packets, service query, service response, and periodic
updates. The following subsections describe how SAP operates:
NetWare client initialization
When a NetWare client is initializing, it needs to locate a server. To do so, the client
broadcasts a Get Nearest Server (GNS) request. At least one router or server can
give a A SAP response, which contains information such as packet type, service
type, and server name and address. The NetWare client can communicate with the
server through the IPX address in the response packet.
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Since the GNS request is broadcast, the client can only get a response from the
server in the local IPX network. To locate a server in another network, the IPX
router can send a RIP request to get the route to the server, and send the route
and service information to the client. In this way, the client can communicate with
a server in another network.
Periodic update of SAP
A server broadcasts a SAP packet to provide the service name and type, and its IPX
address. The IPX router that receives the broadcast will add the service to the
service information database and periodically broadcast such information in the
directly connected networks. The advertisements can thus flood the entire
network.
By default, SAP broadcasts are sent every 60 seconds. Each packet can have up to
7 service information items by default. If a large amount of service information
needs to broadcast, the information can be sent in packets. For example, 20
service information items can be sent in 3 packets.
IPX NetBIOS To enable use of Network Basic Input/Output System (NetBIOS) in a NetWare
environment, Novell provides the following solutions:
As a broadcast, a NetBIOS packet is not routable. Therefore, a certain mechanism
is needed for the routing device to forward such packets. The mechanism used by