AppleTalk Update-Based Routing Protocol

AURP is a tunneling and a routing protocol. It is an enhancement of RTMP. AURP provides the feature of AppleTalk tunneling in TCP/IP. This feature enables two isolated AppleTalk networks to be connected by way of a TCP/IP network. AURP provides update-based routing and reliable delivery of routing information. To reduce the amount of bandwidth, update-based routing sends updates to peer routers only when network routing information changes, rather than sending periodic broadcasts of the routing table.

Like RTMP, AURP also provides distance vector, split-horizon routing. It has a maximum hop count of 15. A tunnel counts as one hop.

NOTE:  The Novell Internet Access Server 4.1 routing software supports the minimal set of AURP features defined in RFC 1504.

Benefits of AURP

AURP is useful in the following scenarios:

• You want to connect isolated AppleTalk networks by way of an existing TCP/IP internetwork. This is referred to as tunneling .
• You prefer to use only IP through your backbone network, but you have isolated AppleTalk networks that you want to connect.
• You have AppleTalk networks connected over a slow WAN link. To minimize bandwidth, AURP sends routing information to peer routers only when there is a change in routing information; yet AURP keeps the routing tables up-to-date.

On a stable network, AppleTalk routers using RTMP broadcast the same information to each other continuously. Because most networks are stable after initial setup, these frequent broadcasts unnecessarily consume bandwidth that could be used to transport more user data. This is particularly noticeable on slow WAN links. Unlike RTMP, AppleTalk routers using the AURP protocol exchange routing information only when a change occurs in the internetwork.

Routing information exchanged with AURP must be communicated reliably. Because only changes are communicated among AURP routers and because this information is not sent periodically (that is, on a set schedule) to peer routers, the possibility of lost information is increased. Therefore, AURP is a transport protocol that provides reliable delivery. It requires the receiving router to acknowledge the receipt of the updates.

NOTE:  The AURP transport ensures reliable delivery of routing packets only. AppleTalk protocols, such as ATP, ASP, PAP, and ADSP, ensure reliable delivery of AppleTalk data packets.

For more information about using AURP for tunneling AppleTalk through IP, including configuration information, refer to "Setting Up" in the routing documentation for AppleTalk.