Is it possible to acheive this task on firewall running iptables and iproute2 (CentOS 4.5) ?
If so, How can I do such thing?
If I do such thing, what will happen to the people behind LAN1 ? Will they get whole 256 kbits/s as before or will they get 256 kbit/s - 64 kbit/s for their internet access?
Yes. use firewall marks and tc.