Netopia Netopia ISDN Router, R310 Netopia Router

E-4 User’s Reference GuideNow look at how two hosts on the LAN interface accessing the same WWW Server on the Internet will work:As you can see, when Workstation A and Workstation B transmit an IP packet to the WWW Server on the Internet, they have unique source IP addresses on the LAN interface but potentially the same source por ts, which in this case is 400. When the Netopia R310 receives these packets, the source IP addresses are substituted with the single globally unique IP address that was acquired on the WAN interface which is 200.1.1.40. Now both IP packets have the exact same source IP address (200.1.1.40) and source ports (400). The way the Netopia R310 is then able to distinguish between the two IP packets is to change the source TCP or UDP ports and keep this information in an internal table. As seen above, the source port for Workstation A has been changed to 5001 and the source port for Workstation B has been changed to 5002.NetopiaRouter

Wkstn A to Netopia

Src IP: 192.168.5.2

Dst IP: 163.176.4.32

Src Port:: 400

Dst Port:: 80

Workstations

A & B

Netopia Router

LAN: 192.168.5.1

WAN: 200.1.1.40

Netopia to ISP Router

Src IP: 200.1.1.40

Dst IP: 163.176.4.32

Src Port:: 5001

Dst Port:: 80

ISP Router to WWW

Src IP: 200.1.1.40

Dst IP: 163.176.4.32

Src Port:: 5001

Dst Port:: 80

WWW to ISP Router

Src IP: 163.176.4.32

Dst IP: 200.1.1.40

Src Port:: 80

Dst Port:: 5001

ISP Router to Netopia

Src IP: 163.176.4.32

Dst IP: 200.1.1.40

Src Port:: 80

Dst Port:: 5001

Netopia to Wkstn A

Src IP: 163.176.4.32

Dst IP: 192.168.5.2

Src Port:: 80

Dst Port:: 400

ISP Router

200.1.1.1

WWW Server

163.176.4.32

Wkstn B to Netopia

Src IP: 192.168.5.3

Dst IP: 163.176.4.32

Src Port:: 400

Dst Port:: 80

Netopia to ISP Router

Src IP: 200.1.1.40

Dst IP: 163.176.4.32

Src Port:: 5002

Dst Port:: 80

ISP Router to WWW

Src IP: 200.1.1.40

Dst IP: 163.176.4.32

Src Port:: 5002

Dst Port:: 80

WWW to ISP Router

Src IP: 163.176.4.32

Dst IP: 200.1.1.40

Src Port:: 80

Dst Port:: 5002

ISP Router to Netopia

Src IP: 163.176.4.32

Dst IP: 200.1.1.40

Src Port:: 80

Dst Port:: 5002

Netopia to Wkstn B

Src IP: 163.176.4.32

Dst IP: 192.168.5.3

Src Port:: 80

Dst Port:: 400