Dear @Vitalijus,

Sometimes it's jumping from one to another wan port. Even if both ports are online, and only one port are configured for this rule. As I understand, I should have access only for one specifit wan port which is configured for this rule? Isn't it? When I set Mode = Only. It's working well. But now if my configured WAN port will be offline, the rule will turn off at all whole route?

In Priority Mode, the rule depends on the online detection result. If all the WANs that you specify are offline, the rule won't take effect.

In Only Mode, the rule always takes effect regardless of the WAN port status or online detection result.

You may configure the Online Detection for the specified WAN ports as Manual mode, and ensure the Load Balance is enabled globally.

If I have 4 WAN ports active, how to set only one main port through which all traffic must travel? Of course only if this port is alive-online.

Sorry that I'm not sure if I understand your question.

Are you trying to make all traffic go through one specific WAN port and the other WANs as backup WANs?

If yes, you could configure the Link Backup function with Failover mode.

Note that the Backup WANs will be online only when the Primary WAN is offline.