Transition mode is a way of configuring Phase 2 routers so that they can operate with Phase 1 routers on an internetwork. This section describes how to configure AppleTalk for NetWare on an internetwork that includes one or more AppleTalk Phase 1 routers.

What the Router Does in Transition Mode

When you configure a router in transition mode, that router is prepared to send out Phase 1-compatible RTMP and NBP packets.

RTMP packets contain information about networks known to the router. By passing this information among themselves every 10 seconds, AppleTalk routers update and maintain their view of the internetwork. NBP packets are used to look up devices on the internetwork.

When the Phase 2 router is not in transition mode, it always sends out Phase 2 RTMP and NBP packets. Phase 2 RTMP packets 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.

Under Phase 2, to find an entity on the internetwork, a node sends an NBP Broadcast Request packet to the closest router. If the requested entity resides on the network directly connected to that router, the NBP Broadcast Request packet is converted into a Lookup packet.

If the requested entity resides on a remote network, the router converts the NBP Broadcast Request packet into a Forward Request packet for each network containing nodes in the zone specified in the NBP Broadcast Request packet. Then the NBP Forward Request packet is transmitted to a router directly connected to the network on which the entity resides. When this router receives the NBP Forward Request packet, it converts it to a Lookup packet and broadcasts it to all nodes in the proper zone on the local network.

When the Phase 2 router is in transition mode, it sends out Phase 1-compatible RTMP packets. A Phase 2 router in transition mode also does not convert Broadcast Request packets into Forward Request packets. Rather, it sends Broadcast Request packets to a router directly connected to the network on which the requested entity resides, whether that network is local or remote.

In transition mode, to avoid extended ranges and zones lists incomprehensible to a Phase 1 router, all Phase 2 routers must observe these addressing constraints:

• On extended networks, the first number in the network range must be equal to the last number in the range, as in 10 to 10.
• On extended networks, the zones list must have only one zone.

How Transition Mode Affects Extended Networks

The addressing constraints in transition mode limit extended networks to 253 devices. If you must support more devices, you cannot use transition mode. Your alternative is to upgrade the Phase 1 routers to AppleTalk Phase 2 so that you do not need to use the transition mode.

Rules for Setting Up a Transition Mode Configuration

When you configure Novell Internet Access Server 4.1 routing software in transition mode for extended networks, the following conditions must be in effect:

• Phase 1 routers typically predate the introduction of AppleTalk Phase 2 and have not been upgraded to support Phase 2. You can connect Phase 1 routers only to nonextended networks (EtherTalk 1.0, ARCnet, and LocalTalk) because Phase 1 does not support extended networks (EtherTalk 2.0, TokenTalk, and FDDITalk). However, having nonextended networks on an internetwork does not necessarily mean that a Phase 1 router is present.
• If the internetwork has Phase 1 routers and you want to keep them installed and configured as Phase 1 routers (rather than upgrade them to Phase 2), you configure all Phase 2 routers on the internetwork in transition mode. When you do that, the Phase 2 router modifies its behavior to operate with a Phase 1 router.
• The Type of Packet Forwarding option must be set to Transition (Phase 1 and 2) from the AppleTalk Configuration screen.
• On extended networks, the first number in the network range must be equal to the last number in the range, as in 10 to 10.
• On extended networks, the zones list must have only one zone.

Nonextended networks should be configured as usual.

As usual, the network number or range you assign to an interface must be unique on the internetwork and consistent for all routers on that network segment. The zone name you assign to an interface must also be consistent for all routers on that network segment.