On my new Gentoo installation I have noticed unexplained download, that wasn't initialize from my part. After using ntop I gain two IP addresses responsible for this. One 10.200.1.128, which according to whois belong to IANA, is sending some data and second 224.0.3.4 is recieving this data. I am not sure about the purpose of this. It happens every day and download about 100MB. In my home network, I have just two PCs with private addresses 192.168.1.10 and 192.168.1.11 and one rooter. Can anybody explain me purpose of this download? Is it security problem or not?

Sorry for bad english.
Thanks.

This is multicast traffic you're seeing on your external network(ISP). It's nothing to worry about.

To be extra safe, you should ingress and egress filtering setup so that your firewall blocks outbound traffic to non-routable IP addresses (such as 10.0.0./8) and incress filtering to block inbound traffic from non-routable ip addresses.