Compatible Systems 5.4 - Manual (Page 292)

286 Appendices
seed router per 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/range.
Unlike TCP/IP, AppleTalk workstations do not have fixed network/node
addresses that need to be configured. Instead, a workstation gets a network
number from the router(s) on the segment it is connected to, and picks an
unused address for its node number through a process called probing.
Probing
When a device comes up on a non-extended AppleTalk network, it will set its
network number to the number seeded on the network, and then try to claim
a node address. It does this by broadcasting a packet to all other nodes on its
segment asking whether the node address is already in use. If another node on
the segment responds, the original node will randomly select another node
address value and try again.
When a device comes up on an extended AppleTalk network, it will set its
network number randomly to one of the numbers in the range seeded on the
network, and then try to claim a node address. It does this by sending out a
packet to all other nodes on its segment asking whether the node address is
already in use. If another node using the same number in the network range
responds, the original node will randomly select another network number and
node address value and try again.
Zones
While network numbers/ranges logically group devices together according to
which network segment they are connected to, AppleTalk zones provide a
way of creating groupings which can correspond to any concept a network
administrator cares to use. This could be the department the devices are used
in, the physical location of the devices, or some other method of categoriza-
tion.
Zones are configured into a router by an administrator, and are logically tied
to a segment and its network number/range by the router. However, the same
zone names can be used on different segments. This gives an administrator
the opportunity to make zone names represent groups of devices which are on
more than one segment. A non-extended network can only have one zone
(which will also be the “default zone” for the segment). An extended network
can have from 1 to 255 zones, one of which will be the default zone.
Once a device has successfully claimed an address, it contacts a router on its
segment and asks for a list of zones for the segment. Unless it has been config-
ured to pick one of the other zones, it will use the “default zone” which is
returned by the router.