3Com CoreBuilder 3500, Implementation Manual

Page: 465 / 592

AppleTalk Zones 465
AppleTalk routers use the Zone Information Protocol (ZIP) to map network
numbers to Zones. Each AppleTalk router maintains a Zone Information
Table (ZIT), which lists the zone-to-network mapping information.
Creating zones within a network reduces the amount of searching that a
router must do to find a resource on the network. For example, to gain
access to a printer on the network, instead of searching the whole
network when you want to print a file to a certain printer, the router
searches for it within a particular zone. You gain access to the printer
more quickly within the zone because the zone includes fewer devices
than the entire intranet.
Important
Considerations
Before administering zones, review the following guidelines and
considerations:
■
Whenever a router discovers a new network, it adds the network to its
RTMP table. It then creates a corresponding ZIT entry with a zone list
of NIL. The ZIP process then requests from the originating router the
corresponding Zones associated with the newly discovered network.
When it receives the associated zones, it then updates the ZIT entry.
■
If the Zone information table contains an entry whose network
number range is not in the RTMP table, it then concludes that the
network is no longer on the Internet, and deletes the networks ZIT
entry. This means, whenever a network is removed from the RTMP
table (whether manually, or though the aging process), the router also
removes ZIT entries that contain the deleted network number.
■
At the time of initialization, the zone information table contains an
entry for each seed interface directly connected to an AppleTalk
network.
■
On a stable AppleTalk network, the ZIP process only occurs when a
new router (new network number) is introduced to the network. ZIP
traffic during any other time can be an indication of network
instability.
■
Whenever a network is aged-out and removed from the routing table,
the corresponding zone information for that network is removed from
the router’s zone information table.
■
Assign zone names for the convenience of end users.