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Avaya P332GT-ML User’s Guide 83
Chapter 12
Avaya P330 Layer 3 Features
Introduction
This section describes the Avaya P330 Layer 3 features. It provides the basic
procedures for configuring the P330 for Layer 3 operation.
Note: Layer 3 features are relevant to P332GT-ML operating in router mode. You
must purchase a Layer 3 preconfigured P332GT-ML module or a Routing License
Key Certificate for the P332GT-ML in order to operate the P332GT-ML in router
mode.
What is Routing?
Routing enables transfer of a data packet from source to destination using a device
called a router. Routing involves two basic activities:
• determining optimal routing paths
• transmitting information packets through an internetwork
Routers use routing tables to determine the routes to particular network
destinations and, in some cases, metrics associated with those routes. Routers
communicate with one another and maintain their routing tables through the
transmission of a variety of messages.
The Routing Update Message is one such message. Routing Updates generally
consist of all or a portion of a routing table. By analyzing Routing Updates from all
routers, a router can build a detailed picture of network topology.
A Link-State Advertisement is another example of a message sent between routers.
Link-State Advertisements inform other routers of the state of the sender's links.
Link information can also be used to build a complete picture of the network's
topology. Once the network topology is understood, routers can determine optimal
routes to network destinations.
Routers can route only those messages that are transmitted in a routable protocol,
such as IP or IPX. Messages in non-routable protocols, such as NetBIOS and LAT,
cannot be routed, but they can be transferred from LAN to LAN via a bridge.
When a router receives a packet, it examines the packet's destination protocol
address. The router then determines whether it knows how to forward the packet to
the next hop. If the router does not know how to forward the packet, it typically
drops the packet unless a default gateway is defined. If the router knows how to