Compatible Systems 5.4 - Manual (Page 289)

Appendices 283
network cable segment. It may sometimes be desirable for redundancy to
have several seed routers on a segment. This is acceptable as long as all seed
routers on the segment are seeding the same network number.
Service Advertising Protocol
Routers participate in allowing end nodes to access IPX services (such as file
servers, print servers, communications servers, etc.) by keeping a list of all of
the services on an IPX internetwork. This list is maintained by examining the
Service Advertising Protocol (SAP) packets which are sent by servers and
other routers on the local segment, and by rebroadcasting this information out
of their other interfaces.
A “split-horizon” technique is used so that routers do not duplicate informa-
tion which is already known on the segment being broadcast to.
Client Machine Addressing
Unlike TCP/IP, IPX workstations do not have fixed network/node addresses
that need to be configured. Instead, a workstation gets its network number
from the router(s) on the segment it is connected to, and uses its Ethernet
address for its node number.
This means that an IPX workstation may have as much as 18 hexadecimal
digits of network/node address. Fortunately for workstation users, the
NetWare client software does the work of discovering the network number
and setting the address. Users only need to install Novell drivers to be able to
use the IPX protocols over their network.
Routers which support IPX can use any of four “frame types” to send IPX
packets. Each frame type organizes the IPX information in a network packet
(i.e. frame) in a slightly different fashion. Although the basic information
may be the same, clients or servers using different frame types cannot
communicate with each other without an intermediate translation occurring
between frame types. This translation is called “transitional routing,” and is
one of the functions that can be performed by routers.
The four IPX frame types are:
• Ethernet_Type_II
• Ethernet_802.3 (Raw)
• Ethernet_802.2
• Ethernet_SNAP
Older versions of NetWare defaulted to the 802.3 Raw frame type, whereas
NetWare 4.0 uses the 802.2 frame type.