Compatible Systems 5.4 - Manual (Page 290)

284 Appendices
For this reason, the default configuration for Compatible Systems routers
which support IPX has both 802.3 Raw and 802.2 set to autoseed (they will
come up regardless of whether there is a server on line or not) and the other
two frame types set to non-seed (they won’t come up unless they “hear”
another router using this frame type.
This autoseeding default router configuration simplifies administration of the
router since IPX can be routed right out of the box without any configuration.
To determine a network number to use for autoseeding, a router listens to the
network for several RIP periods, and then examines its routing table (which
is filled in with information from RIP packets), and picks an unused number.
AppleTalk 101
v Note: This is a very brief introduction to AppleTalk networking. For more
in-depth information, the definitive reference is Gursharan Sidhu et al’s
Inside AppleTalk (Addison-Wesley Publishing). This book provides an
in-depth look at the AppleTalk protocol suite and AppleTalk routing.
AppleTalk Routing Basics
All routable protocols work by dividing the physical devices on a network
into logical groups. A logical group will typically consist of all of the
machines on a physical network segment (such as an Ethernet segment).
Each group of devices is assigned a unique “network number” (or a range of
network numbers) which represents that particular group to all of the routers
on the network. Packets which are sent between members of the same group
are simply sent directly from one member to another.
Packets which must go between devices belonging to two different groups
travel through routers, which forward them along an optimal path.
By examining the destination network number in a packet that must be
forwarded, and by using information that routers automatically pass between
themselves in AppleTalk Routing Table Maintenance Protocol (RTMP)
packets, any router can determine the optimal path for forwarding packets
from one group to another.
This scheme relies on the fact that each segment is assigned a unique network
number/range. If not, the routers have no way of knowing which of the phys-
ical segments with that number should actually receive a packet.