Introduction to Data Communications
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42c. Router Segment to Segment Characteristics

Routers that only know Novell IPX (Internetwork Packet Exchange) will not forward Unix's IP (Internetwork Packet) PDUs and vice versa. Routers only see the Network Layer protocol that they have been configured for. This means that a network can have multiple protocols running on it: SPX/IPX, TCP/IP, Appletalk, XNS, etc..

In the following network, Router #3 is a Novell SPX/IPX router, it only sees the Network Layer protocol IPX. This means that any TCP/IP PDUs will not pass through, the router does not recognize the PDUs and doesn't know what to do with them.

Routers #1 & #2 are TCP/IP routers, they recognize only IP protocols. This keeps SPX/IPX traffic off of "Segment 300". This is in quotations because TCP/IP has a different network numbering scheme than IPX.

Important Point: Routers allow network traffic to be isolated or segmented based on the Network Layer Protocol. This provides a functional segmentation of the network.

Routers that only can see 1 protocol are called Protocol Dependent Routers. Routers that can see many different protocols (2 or more) are called Multiprotocol Routers.

Introduction to Data Communications
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