Bay Networks 3395A, Configuration Manual

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IP and IPX Routing
893-826-A 1-17
IP and IPX Routing
Large Internet (IP) or Novell NetWare (IPX) networks with many hosts, file
servers, or other devices that offer user services are often subdivided into
smaller, separate networks to improve overall network performance and make
the network easier to manage. These subnetworks, or subnets, can exist in the
local or distributed locations. Sites with a small number of devices that are
connected through routers or gateways to larger IP or IPX networks can also be
divided into subnets.
The communication server contains a list of routes. This list is called a routing
table. The routes specify a preferred path where the communication server can
send traffic bound for a particular destination.
The Multiprotocol Communication Server software supports some IP and IPX
routing capabilities:
• Communication servers perform limited IP routing.
Servers collect ICMP (Internet Control Message Protocol) messages,
which allow the server to “learn” IP routes in order to send packets to the
appropriate destination. Servers can also be configured with a
manager-specified, or “static” IP route.
• Communication servers act as “full” IPX routers.
Servers collect IPX RIP (Routing Information Protocol) and SAP (Service
Advertising Protocol) messages, which allow the server to “learn” IPX
routes in order to send packets to the appropriate destination. Servers also
broadcast IPX RIP and SAP messages and can be configured with a
manager-specified, or “static” IPX route.
Dynamic Routing
The IP and IPX protocols support communication between devices on separate
subnetworks through routers or gateways that are connected to two or more of
the subnetworks. The routers and gateways communicate among themselves,
forwarding network traffic to each other as well as between networks,
according to their routing protocol. The gateways also select the most efficient
path to a destination for communications sent by a host or communication
server. This is called “dynamic routing.”
As conditions change, the path to a destination may also change. For example,
when the Internet route changes, the hosts and communication server are
informed, through ICMP routing messages, that the packets they sent to a
particular gateway have been forwarded to another gateway on the same
network. As long as a host or communication server sends traffic to a gateway
that forwards traffic when necessary, the sender can be assured that the packets
will eventually reach the destination. Internet routes to a destination that the
server obtains in this manner are called learned Internet routes. Similar
activities occur on IPX networks, where IPX RIP and SAP messages inform the
communication server of changes.