This is my network: I start FTP transfer (3Gb file) from WEB server 1 to WEB server 2. The speed was around 60Mbit/s and after few minutes mikrotik crash. PPPoE clients can not connect. I have to restart Mikrotik.

When I create rule in queues to limit the speed to 20Mbit/s it is OK.

Why mikrotik crash for "high speeds"?

I'm using:
CPU: intel 2G
RAM: 512 (free: 434Mb)
3 Lan interfaces:
1 - WEB server 1 (internet gateway)
2 - Local WEB server 2
3 - PPPoE clients

The problem is not from MT OS side, please check your hardware(Lan cards and switchs between your optical network).

Thanks

I do not think that it is hardware problem because as speed go up, CPU also go UP. So.... if the speed is limited on 20Mb and 400 PPPoE users connected CPU usage is around 60%. If the speed is more, CPU usage is 100%.

I think that it is normal (because firewall have to "process" more data). Also, this is like DoS attack.

I am not 100% sure but somewhere I'd read that mikrotik can support 132 mbps data transfer.
Maybe it causes the problem.

Rafiq...

on our core routers (routing, w/o ppp) we have speeds up to 500Mbps - uptime is from reboot to reboot (upgrading, or electricity fails) =)

May be because I have a lot of firewall definitions and it use processor.

The probably is likely due to a bug in a NIC driver (maybe a race condition). The probability of hitting the bug increases with the increase in interrupt frequency which is driven by traffic levels. Try different NIC's. I like the Intel Pro/1000 Quad-port myself.