What is the MTU/MRU/MRRU configuration on router? What exact rules did you add to make it work again?
What should be on client side and ppooe_servers? 1480/1480/1600 are these correct ?
Have you tried to sniff packets on another device behind this router to see MSS when Mangle rules are not there and when they are? Are you sure that change-tcp-mss is enabled on PPP Profile used for connection?
i have also no any mangle rule on firewall and change-tcp-mss is enabled on PPP Profile on the ppooe_servers.
how can i understand if it is work correctly ?
You will know because some web sites will load, and others won't. The behavior of your customer connections will be strange and unpredictable. Like most MTU issues when they occur.
My problem stems from already having made PPPoE servers, (with default MT settings for mtu and mss clamping). Then when I upgraded, my PPPoE customers don't work any more. So going from defaults, to defaults, something has broken in the code from MT's side of things. Although, they apparently don't think so, and I'm supposed to figure it out for them I guess.
My customers were magically fixed when I added the mangle rules back in that the newer version strips out. As those rules previously were dynamically added by MT. New versions exclude them it seems..