How Does Transition Mode Affect Extended Networks?
The addressing constraints in Transition Mode mean that extended networks are limited to 253 devices. If you must support more than 253 EtherTalk 2.0 or TokenTalk devices, you cannot use Transition Mode. Your alternative is to upgrade the Phase 1 routers to AppleTalk Phase 2.
What Does the Router Do in Transition Mode?
When you configure a router in Transition Mode, the router is prepared to send out Phase 1-compatible RTMP packets on its nonextended interfaces.
RTMP packets contain information about all networks known to the router. AppleTalk routers pass this information among themselves every ten seconds, updating and maintaining their view of the internet.
When the Phase 2 router is not in Transition Mode, it always sends out Phase 2 RTMP packets. Phase 2 RTMP packets are different from Phase 1 RTMP packets, and can contain information about extended networks. A Phase 1 router cannot read the Phase 2 packets and cannot incorporate the Phase 2 information into its routing tables.
When the Phase 2 router is in Transition Mode and it receives a Phase 1 RTMP packet on one of its nonextended interfaces, it sends out Phase 1-compatible RTMP packets on that network. The network information contained in these packets cannot include extended ranges and zones lists, which means that all extended networks (EtherTalk 2.0 or TokenTalk) on the entire AppleTalk internet must be configured with a network range of one (for example, 10-10), and a zones list of one (for example, "My zone").
An Internet That Does Not Require Transition Mode
Figure 77 shows a basic AppleTalk Phase 2 internet, in which all routers support AppleTalk Phase 2. The routers on this internet do not require Transition Mode.
Figure 77
An Internet That Does Not Require Transition Routing
In Figure B-1, two servers are running NetWare for Macintosh, and each server supports multiple Phase 2 interfaces. The TokenTalk and EtherTalk 2.0 networks can use extended network ranges, so they can support as many devices as you need (see AppleTalk Phase 2 Networks and Zonesfor details.).
An Internet That Requires Transition Mode
Figure 78 shows an internet similar to the one shown in Figure 77, except that a Phase 1 router is present on the EtherTalk 1.0 network. The Phase 2 routers on this internet must be configured in Transition Mode.
Figure 78
Transition Routing Required for Phase 1 Routers
In Figure 78, two servers are running NetWare for Macintosh, and each server supports multiple Phase 2 interfaces. However, there is a Phase 1 router present on the EtherTalk 1.0 network. In this internet, both Phase 2 routers must be in Transition Mode. The TokenTalk and EtherTalk 2.0 networks cannot use extended network ranges, so they will be limited to 253 nodes on each network.