TITLE
    AppleTalk Phase 2: Obtaining Node Number on Startup
Article ID:
Created:
Modified: 		5955
8/28/90
8/28/90
TOPIC



    Under the AppleTalk Phase 2 protocol specification, a node remembers the node
    number previously assigned to it and that it is stored in the Macintosh. Does
    the Macintosh also remember the last network number it was associated with, and
    where is that number stored? If the network number is not stored, does the
    resolution begin at the base of the network range?

DISCUSSION

    This information is on page 8 of the "AppleTalk Phase 2 Protocol
    Specification":

    Obtaining a provisional address

    Obtaining a provisional address upon startup is accomplished in two different
    ways depending on whether the node has previously saved an address in parameter
    RAM. An address saved in PRAM consists of two parts: the 16-bit network
    number, denoted $nnnn, and the 8-bit node ID, denote $yy. The concatenated
    24-bit address value of [network number, node ID] is denoted $nnnnyy.

    If no address was previously saved in PRAM:

    Upon starting up when no information is saved in parameter RAM, a node will
    randomly select a provisional network number $FFnn in the startup range. This
    range is specified to be $FF00 to $FFFE inclusive (most significant byte
    first). The node then also randomly selects a node ID $yy (yy cannot be $00,
    $FE, $FF). As in AppleTalk Phase 1, the node must first use AARP to ensure
    that $FFnnyy is not in use by any other node on the network. If another node
    is already using this address, the node should try all other possibilities for
    $FFnnyy until a valid provisional address is obtained.

    If an address was saved in PRAM:

    If there is a saved 24-bit address of the form $nnnnyy in PRAM, the node can
    use it as the provisional address. The node must use AARP to ensure that this
    address is not in use by any other node. If another node is already using this
    address, the node should try all other possibilities for yy (yy cannot be $00,
    $FE, $FF) keeping nnnn the same until all possibilities are exhausted (nnnn is
    probably a valid network number for this network unless the node has been moved
    from another network).

    If all possibilities are exhausted, the node must select a new address as if
    none was previously saved in PRAM (as described in the previous section).



Document Information
Product Area: Communications-Networking
Category: Protocol and File Format Information
Sub Category: General Topics
Keywords:

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