Long story short, if you are using MTU 9000 you better check every component including virtual networks in between, so it was my fault, I thought underlying card and bond had already MTU 9000 applied so missed this little step to check virtual stuff, ping with MTU 9000 does not fail by the way, anyways it was my fault, I don't even know if xen allows you to apply MTU 9000 to the network via API, Thanks, Sam
