# Modbus TCP - A slave in one physical chain acting as a master in another

**URL:** <https://forum.inductiveautomation.com/t/modbus-tcp-a-slave-in-one-physical-chain-acting-as-a-master-in-another/109558>\
**Category:** Ignition\
**Tags:** modbus, perspective\
**Created:** [August 9, 2025, 9:00pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-a-slave-in-one-physical-chain-acting-as-a-master-in-another/109558 "2025-08-09T21:00:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Melby\_Miraval](https://avatars.discourse-cdn.com/v4/letter/m/bc8723/32.png) [@Melby\_Miraval](https://forum.inductiveautomation.com/u/Melby_Miraval)\
**Post date:** [August 9, 2025, 9:00pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-a-slave-in-one-physical-chain-acting-as-a-master-in-another/109558/1 "2025-08-09T21:00:41Z")

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I have 3 Modbus RTU devices connecting to the Ignition SCADA via a RTU to TCP Gateway. I am using Modbus TCP. I know I can reach the tags from these devices using

[Gateway][slaveID].tagpath

One of those 3 RTU devices has other 5 RTU devices connected to it. My question is how can I address those 5 RTU devices?

Thank you!!

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**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\
**Post date:** [August 9, 2025, 9:27pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-a-slave-in-one-physical-chain-acting-as-a-master-in-another/109558/2 "2025-08-09T21:27:30Z")

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How do you already connect to them using Modbus TCP?

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [August 9, 2025, 9:31pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-a-slave-in-one-physical-chain-acting-as-a-master-in-another/109558/3 "2025-08-09T21:31:52Z")

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There’s really only two ways this could play out, and you’ll have to tell us:

1. those other 5 slave devices are on the same multidrop serial line as the intermediate one, in which case they’re just going to have their own slave id that you should know and just need to address
2. they map into the process image / memory of the intermediate device in some proprietary manner that hopefully you have documentation for, and then you would just access corresponding registers in the intermediate device

Modbus doesn’t have multi-layer/hop addressing or routing.