I installed a FreeBSD 10.0 server(IP:10.1.2.3), and want to send packets to remote clients, with fake source ip, such as:

```
socket_sendto($socket $data, $length, 0, $ip, $port)

```

$data contains IP header, where i specify my "fake ip" here.

The questions is:

1. if i specify the IP to C class, everything goes well(below success):

```
10.1.2.4
10.1.3.5

```
2. if i specify the IP to B or A class, nothing send to destination(below failed):

```
10.2.1.2
11.1.2.3

```

So, how can i resolve the issue? 

Btw i already modified sysctl.conf to :

```
  net.inet.ip.forwarding=1
  net.inet6.ip6.forwarding=1
  net.inet.ip.fastforwarding=1

```

Sorry for poor English.