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Chapter 2

Protocol Attributes

administrator's ability to create multiple logical networks within the same
segment. There must be a better way! Thankfully, Apple thought so, too.
Look at some changes made for AppleTalk Phase 2 (see Table 2.16).

With Phase 2, there can be an unlimited number of network addresses per

segment. In addition, there are ample node addresses available, despite the
fact that network addresses are still only eight bits long.

There really isn't an unlimited number of networks available per segment--

you're still limited by the 16-bit network portion of the address, giving you

approximately 65,000 potential networks. It's highly unlikely that you'd ever

need anywhere near 65,000 network addresses for a single network, however.

In addition, you can now have multiple zones per network, allowing you

to create multiple logical networks (zones) within a single network segment.

As is the case with IP, there are a few reserved network and node

addresses. Network address 0 (zero) is reserved for use by nodes that haven't
yet learned their segment's address, so it can't be assigned. Node addresses
254 and 255 are also reserved and can't be assigned to nodes.

The technique used by AppleTalk Phase 2 to assign multiple network

addresses to a single segment is called extended addressing. Instead of having
a single network address on a segment, you can assign a range--an exten-
sion--of addresses to a segment. Here's an example: A non-extended address
for a segment can be network 100, and an extended address for the same seg-
ment can be network 100110--a range of 11 network addresses. What if
you need even more node addresses, however? Well, how about network
1001000 (901 network addresses)? Need fewer node addresses? Try net-
work 100100 (one network address). All you have to do is specify a range

T A B L E 2 . 1 6

AppleTalk Phase 2 Addressing

Item

Amount

Network addresses per segment

Unlimited

Host addresses per network

Unlimited

Server addresses per network

Unlimited

Zones per network

255

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