^C[monitor] 2024/09/18 16:38:25.210892 monitor.go:161: INFO: Signal 2 received; exiting
[N74QT] 2024/09/18 16:38:26.021916 tcp_listen.go:120: INFO: TCP listener (10.x.x.x:22000) shutting down
[N74QT] 2024/09/18 16:38:26.022683 syncthing.go:351: INFO: Exiting
```
---
### Author:  [@AudriusButkevicius](https://forum.syncthing.net/u/AudriusButkevicius)
#### Post date: [September 18, 2024, 1:43pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/12 "2024-09-18T13:43:30Z")
We always add a :0 for good measure.
---
### Author:  [@firesnake](https://forum.syncthing.net/u/firesnake)
#### Post date: [September 18, 2024, 1:44pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/13 "2024-09-18T13:44:00Z")
can it be disabled? this will multiply by hundreds of devices resulting in repeated loops of tcp resets, and that would be anything but “good measure” for my network
---
### Author:  [@AudriusButkevicius](https://forum.syncthing.net/u/AudriusButkevicius)
#### Post date: [September 18, 2024, 3:50pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/14 "2024-09-18T15:50:10Z")
You can’t. It’s 2 packets, not sure why you are so concerned.
---
### Author:  [@firesnake](https://forum.syncthing.net/u/firesnake)
#### Post date: [September 18, 2024, 3:51pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/15 "2024-09-18T15:51:27Z")
it’s 2 packets multiplied by hundreds or more devices repeated all over. I need to reduce traffic to minimum because it’s a high latency low bandwith infrastructure
plus, I don’t think it’s normal for clients to search for each other on invalid ports in an infinite loop. at least open/bind to that port you are announcing.
---
### Author:  [@AudriusButkevicius](https://forum.syncthing.net/u/AudriusButkevicius)
#### Post date: [September 18, 2024, 4:00pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/16 "2024-09-18T16:00:34Z")
Feels like you need specialised software if you care about that. Syncthing chats quite a lot willy nilly, and priority is connectivity rather than minimal bandwidth.
---
### Author:  [@firesnake](https://forum.syncthing.net/u/firesnake)
#### Post date: [September 18, 2024, 4:05pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/17 "2024-09-18T16:05:45Z")
still remains a valid point that clients are instructed to connect to other clients to ports on which they don’t listen. that’s got nothing to do with being chatty, but sounds rather a design bug to me.
it’s like meeting a person and telling them call me on this number, and oh, look me up in the directory, but hey, you might find an invalid number of me there.
---
### Author:  [@AudriusButkevicius](https://forum.syncthing.net/u/AudriusButkevicius)
#### Post date: [September 18, 2024, 4:15pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/18 "2024-09-18T16:15:59Z")
Clients don’t know what ports the nat mapped for them, hence the notion of :0, which gets replaced by the outgoing connection port by the discovery server.
---
### Author:  [@Nummer378](https://forum.syncthing.net/u/Nummer378)
#### Post date: [September 18, 2024, 4:50pm UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/19 "2024-09-18T16:50:18Z")
So, as already mentioned port 0 gets replaced by the dialing (source) port of the announce, which _should_ be a valid port that syncthing also listens on (like 22000). This is done via TCP port reuse, so that the outgoing port is the same as the incoming port (i.e. you’ve both a TCP client and a TCP server socket on the same port). This causes the annoucement to be sent from port 22000, which your NAT might then remap to whatever. The discovery server records the NAT-mapped port so that hole punching knows where to knock.
In your case this goes wrong (which can happen due to unsupported operating systems, network interface or routing specifics), in that case syncthing falls back to letting the operating system choose an outgoing port. This port is obviously not setup for incoming connections, so it causes the behaviour you’re seeing. This is not the intended behaviour of the announcement, but rather the result of TCP port reusing not working properly for some reason.
There’s debug logging in syncthing which logs TCP port reuse problems, so data from that could help.
---
### Author:  [@firesnake](https://forum.syncthing.net/u/firesnake)
#### Post date: [September 20, 2024, 11:21am UTC](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814/20 "2024-09-20T11:21:06Z")
> [@Nummer378](#):
>
> which your NAT might then remap
there is no nat involved. the nat is disabled in configuration. there is direct routing via isolated network. there is no relay enabled. there is no local announcement enabled. there is no firewall.
**it’s just plain simple host A to host B communication via standard router.**
I fail to see any logical reason to still announce :0 in this case.
[Next page](https://forum.syncthing.net/t/how-to-prevent-devices-from-announcing-themselves-to-stdiscosrv-with-random-ports-in-addition-to-port-22000-while-nat-and-lan-discovery-are-already-disabled/22814.md?page=2)