Editing: Unravelling_AppleTalk_Network_Numbers

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title:Unravelling AppleTalk Network Numbers
author:@europlus@europlus.zone
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In AIR 3.0 and jRouter (and any other AppleTalk router systems), network segments are identified by network numbers.

Whether the segment is a LocalTalk (Printer or Modem port) or an EtherTalk (Ethernet port) network segment, any network numbers assigned to those segments **must be** unique across the whole AppleTalk “internet” (internetwork, of which GlobalTalk is an example).

Under the AppleTalk Phase 2 standard, each network number can host up to 253 devices, and there are 65,279 network numbers available.

If you expect a given segment will never be larger than 253 devices, there is no point assigning any more than 1 number to it – this includes EtherTalk networks, which are assigned a range of numbers.

That range, however, can be a range of one network number (e.g. the Airaga node’s EtherTalk segment is defined as having a range of “19680-19680” – I will not be adding enough devices to that segment to need any more).

If an AIR router has EtherTalk and LocalTalk segments, each segment must have a number or a range which not only mustn’t overlap locally, but must be unique, once again, across the GlobalTalk network.

For example, if I “claimed” and assigned the range 19680-19685 for the Airaga EtherTalk segment, I couldn’t use 19685 for one of my LocalTalk zones.

Note here that LocalTalk network numbers and EtherTalk network ranges do not have to be contiguous. I could have 1968 for one LocalTalk segment, 2025 for another LocalTalk segment, and 19680-19680 for my EtherTalk segment, all connected to GlobalTalk through the one AIR router.

While it is true we’ll not run out of numbers, I consider it a courtesy to only “take what you need”.

Some networks **do** need more than 1, 2, or 3 network numbers if they have multiple segments (there are several routers which bring such complex networks onto GlobalTalk, but they are far from the norm), and this is still an honour system where admins are expected to act cooperatively.

One last point – zones are separate to network numbers. Zones do not have to be unique, so different network numbers can have the same zones defined for them (e.g. you’ll see the GlobalGaming zone occasionally appears i non-contiguous network numbers/ranges).

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