Understanding the network.pdf - Back to Home

Figure 3.3. The AppleTalk address structure.
The network and node addresses are assigned dynamically when the
node joins the network.
When a node first joins the network, it acquires a provisional address.
The node address portion is randomly selected from the number
range 1 to 254 (0 and 255 are reserved). The network portion is
assigned by the Layer 2 protocol (ELAP, LLAP, TTAP, or FDAP) from a
reserved class of network addresses spanning from 65,280 (FFF0
hexidecimal) to 65,534 (FFFE hexidecimal). These network addresses
are recognized by all AppleTalk nodes as provisional addresses. After
the provisional address is acquired, a permanent address is needed.
The node then sends a GetNetInfo request using the Zone
Information Protocol (ZIP). If a router responds, the available
network number(s) is returned with the ZIP reply. The node then uses
that network number, generates another random node ID, and
broadcasts this number across the segment. If no nodes respond
claiming rights to that address, the node uses the address. If a node
responds claiming ownership to that ID, the node must repeat the
node generation and validation process until it selects a node address
that is not in use.
If no router is available or the network type is Phase 1, the network
address is set to 0 and the node sends a broadcast to see if its address
conflicts with another node. If it doesn't, it becomes the node's
permanent address. After a node address is acquired, it is stored by
the end-station for later use. If the node leaves the network and
returns at a later point, it attempts to validate its previous address. If
there are no conflicts, it continues to use the address.