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General Networking/Lan/Wan/IP Pass Through versus IP Port Forwarding


Hello Sudhanshu
Thank you in advance for time and help.
I have questions on IP Pass Through versus IP Port Forwarding and Dynamic versus Static as I donít have a clear understanding. Please, let us start with IP Pass Through versus IP Port Forwarding.
I have a SIM with a mobile IP Address from AT&T and using a Digi Connect WAN 3G wireless modem with one Ethernet port.
I think IP Pass Through acts as a bridge between the modem and a third party device (e.g. camera) and shares the IP Address with a single device and it acts as a router behind the modem.
I think IP Port Forwarding takes incoming data and forward to a specific port. In this case, I think you would use a modem with one Ethernet port for two cameras and one IP Address with two different port numbers (e.g. 8080 and 9191). Or with one modem with two Ethernet ports for two cameras and one IP Address with two different port numbers.
I found out I can use either IP Pass Through or IP Port Forwarding and it works the same but I maybe using it incorrectly.
When to use IP Pass Through, for a single device? When to IP Port Forwarding, for multiple devices?

Harry....I know the challenge that you are facing. Both have been used interchangeably very often and works almost the same. So generally people don;t realize what they are using and what they should have used. Port forwarding is used when you want to share one IP address among several devices and in this connection is established end to end over the socket (ip address + port). In IP passthrough the public IP is assigned to another device as you have mentioned. This IP once passed can also be used for port forwarding just in case you want to use that for any specific communication. Port forwarding is generally used when all external communication is to be restricted to a single IP.
In short, IP passthrough will have a connection break & for one device whereas its end to end in and for multiple in port forwarding.

Hope this helps.

General Networking/Lan/Wan

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Sudhanshu Gupta


Any question related to IP routing protocols - BGP/OSPF/IGRP/EIGRP/RIP, HSRP. Bridging/DLSW, Cisco routers and Switches, LAN/WAN installation and monitoring.


I have about 14 yeras of experience in networking. I am an MCSE and CCIE (7334).

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