Limit on connections to services on the router?

[ivo]

Hello,

I had version 17 (LEDE) running on my APU board (4 cores, 2GB RAM) and ran into the issue that the zabbix agent I am running would not respond from time to time. To test this I started requesting Zabbix data and curl the uhttp every 500 msecs from another host and the problem intensified.
The zabbix logs say the agent is idle and tcpdump on the port shows packages stop coming in.
The problem happens every few minutes for about 30 seconds with the 500 ms test and about 3 times a day with just the zabbix server connecting.

Whenever zabbix_agent is unresponsive, uhttpd is not responding either (curl timing out).

When this happens, routing is not affected and there is no problem seen by devices connecting to the internet.

Is there some limit for connections to services on the router that I may be running into that I could up?
There are no spikes in CPU load (Load average is 0.03) and active connections is at about 24%.

Any help would be appreciated,
Ivo

[vgaetera]

https://openwrt.org/docs/guide-user/firewall/firewall_configuration#defaults

syn_flood
synflood_protect

iptables-save -c | grep -e syn_flood

[ivo]

Thanks! That did the trick.

What I don't understand: Should the protection not just count un-acked connections?

[vgaetera]

That feature is known to be problematic and doesn't provide the necessary options to separate LAN and WAN connections.