# Multiple drone simulation gazebo GCS port **URL:** \ **Category:** PX4 Autopilot\ **Created:** [August 18, 2024, 2:14pm UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254 "2024-08-18T14:14:27Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Ryuu](https://discuss.px4.io/user_avatar/discuss.px4.io/ryuu/32/17021_2.png) [@Ryuu](https://discuss.px4.io/u/Ryuu)\ **Post date:** [August 18, 2024, 2:14pm UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254/1 "2024-08-18T14:14:27Z")
Hi i’m pretty new with multiple vehicle simulation in the gazebo (no ROS). so I have a question, if I ran **multiple vehicles do I need to separate GCS port for each instance like 14550 and 14550 + instance?** In my case if I run Tools/simulation/gazebo-classic/sitl\_multiple\_run1.sh -t px4\_sitl\_default -s iris:1,plane:1 -n 2 by by default, it seems all traffic goes out to port 14550. ---
**Author:** ![Ryuu](https://discuss.px4.io/user_avatar/discuss.px4.io/ryuu/32/17021_2.png) [@Ryuu](https://discuss.px4.io/u/Ryuu)\ **Post date:** [August 18, 2024, 2:20pm UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254/2 "2024-08-18T14:20:00Z")
if i simulate 2 vehicles and open QGC in same local machine, QGC will auto-connect to the vehicle (I guess UDP 14550). but if I want to connect to the simulation from another Machine same lan, I used mavlink-router to forward data from port 14550 to another port i.e 14552 and connect QGC in that machine. but now the simulation not work as expected first error when I upload the plan. after a few attempts I able to upload ![image](https://discuss.px4.io/uploads/default/original/3X/0/8/0846f4a15c364938b9fca4a401ed61a6b5c552e1.jpeg) ---
**Author:** ![Ryuu](https://discuss.px4.io/user_avatar/discuss.px4.io/ryuu/32/17021_2.png) [@Ryuu](https://discuss.px4.io/u/Ryuu)\ **Post date:** [August 19, 2024, 1:22am UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254/3 "2024-08-19T01:22:22Z")
@JulianOes have you ever got a problem like that? i used the latest px4 version and gazebo-classic ---
**Author:** ![hamishwillee](https://discuss.px4.io/user_avatar/discuss.px4.io/hamishwillee/32/3469_2.png) [@hamishwillee](https://discuss.px4.io/u/hamishwillee)\ **Post date:** [August 21, 2024, 12:13am UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254/4 "2024-08-21T00:13:24Z")
Simulation without ROS on Gazebo classic is covered in [Multi-Vehicle Simulation with Gazebo Classic | PX4 Guide (main)](https://docs.px4.io/main/en/sim_gazebo_classic/multi_vehicle_simulation.html#multiple-vehicle-with-gazebo-classic) The docs indicate: > Each vehicle instance is allocated a unique MAVLink system id (2, 3, 4, etc.). MAVLink system id 1 is skipped in order to have consistency among [namespaces](https://docs.px4.io/main/en/ros2/multi_vehicle.html#principle-of-operation). Vehicle instances are accessed from sequentially allocated PX4 remote UDP ports: `14541` - `14548` (additional instances are all accessed using the same remote UDP port: `14549` ). Looking at those IDs I think that those are links for a companion computer to connect to, NOT a GCS. I _suspect_ that the GCS expects all instances to be on 14550. That would make sense for testing via QGC so you don’t have to set up multiple connections? @Jaeyoung-Lim Can you advise? Specifically, if you have multi-vehicle sim in Gazebo are there separate ports for companion and GCS? For GCS do you have “multiple UDP ports” too? How is this expected to work? ---
**Author:** ![Ryuu](https://discuss.px4.io/user_avatar/discuss.px4.io/ryuu/32/17021_2.png) [@Ryuu](https://discuss.px4.io/u/Ryuu)\ **Post date:** [August 21, 2024, 7:49am UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254/5 "2024-08-21T07:49:09Z")
because i want to connect GCS in other machine so that i have to forward mavlink data to other IP address use **mavlink-routed**. however the message seem dropped frequently ![image](https://discuss.px4.io/uploads/default/original/3X/e/b/eb8c5ea92dc0b25c9f87a99608fc8d84f0c232f1.png) so that’s why i was thinking about separate ports for companion and GCS. i changed > to **mavlink start -x -u $udp\_gcs\_port\_local -r 4000000 -f -o $((14551+px4\_instance))** and update the typhoon\_h480.sdf and plane.sdf file ![image](https://discuss.px4.io/uploads/default/original/3X/b/0/b0cab6651fe7e1fcbf91302ec3e67d6eff980fb8.png) ---
**Author:** ![hamishwillee](https://discuss.px4.io/user_avatar/discuss.px4.io/hamishwillee/32/3469_2.png) [@hamishwillee](https://discuss.px4.io/u/hamishwillee)\ **Post date:** [August 21, 2024, 11:45pm UTC](https://discuss.px4.io/t/multiple-drone-simulation-gazebo-gcs-port/40254/6 "2024-08-21T23:45:48Z")
> [@Ryuu](#): > > because i want to connect GCS in other machine so that i have to forward mavlink data to other Not an expert, but I don’t think you need to do this to connect GCS to another machine on same network. In QGC “Applications Settings” \> Comms Links you can add a new comms link. Then use the same port, but specify the Server address of the remote machine. I use this approach on Windows with WSL2 to connect to simulation running in WSL2 from my host - see [Windows Development Environment (WSL2-Based) | PX4 Guide (main)](https://docs.px4.io/main/en/dev_setup/dev_env_windows_wsl.html#qgroundcontrol-on-windows)