3Com REMOTE ACCESS SYSTEM 1500, Руководство по управлению

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92 C
HAPTER
7: LAN-
TO
-LAN R
OUTING
Overview
The SuperStack II Remote Access System (RAS) 1500 can perform IP
routing with a remote RAS 1500 or third-party router over analog or
Integrated Services Digital Network (ISDN) digital lines (Figure 11).
Figure 11 LAN-to-LAN Routing with the RAS 1500
The Difference
Between Bridging
and Routing
Routing and bridging are very similar: they move packets between
networks. When a packet arrives at a bridge or a router, the device uses
tables to determine where the packet belongs.
A major difference between routing and bridging is the layer at which
each works.
■
Bridges use hardware address (Data Link layer) to determine the
destination of the packet.
■
Routers use network address (Network layer) to determine the
destination of the packet.
This chapter discusses configuring the RAS 1500 for routing. For a
discussion of bridging, refer to Chapter 8, “Bridging with the RAS 1500.”
When a packet arrives at a router, the router analyzes the packet for the
network address, such as an IP, IPX, or AppleTalk address.