There’s a routerboard 750g connected to a cisco 800 series router which connected to service provider with ATM over IP.
when i change the constant bit rate (cbr) of virtual circuit (on ATM) to 512 (it means 512kb/s), then the rb750g will ping correctly but winbox will not work from the world and the network behind of the routerboard will disconnect from Internet!
i played with MTU/MRU and … which cisco recommend but it won’t work. the problem will occur when new connection want to initiate. it means by example, when the cbr on 256 and establish a sample connection by routerOS, changing the cbr to 512 will not disconnect that but new connections will not establish! change it back to 256 will fix but i need 512kb!!!