Forwarding just in case anyone is familiar with this on CentOS, thanks! -- Hello, Just found that net.ipv4.ip_local_port_range has different behavior between RHEL releases: until v6 although you have multiple source IPs you can only use a fixed number of local ports, seems that "ip_local_port_range" is a global configuration or limitation. On RHEL-6 kernel (testing with 2.6.32-279) you can bind() to N local ports per source IP, it's a per-IP limit: total ports = ip_local_port_range x source IP. The problem is that on RHEL-5 and 4 you can only make ip_local_port_range outgoing connections and you can't use different source IPs trick to increase this limitation. I have been testing and vanilla 2.6.32 kernel and other Linux distributions like Debian doesn't support this. What has been changed/patched on RHEL-6 to allow this? Santi Saez