Why my setting does not work?

lab            mypc      server
7000    ->  5900
1080    ->  10800
            10800 -> internet
            15900 -> 5900
            22 -> github:22
            
rinitd runs at lab pc
1081 -> 1080
17000 -> 7000
            
test

pcx --VNC-> lab:17000 to connect mypc                     ok

 pcx: VNC connect lab:17000                            VNC client protocal
 lab: rinitd redirect 17000 to 7000                    rinitd tunnel
 lab: 7000 redirect via ssh tunnel to mypc:5900     ssh tunnel
 mypc: 5900 is VNC server                            VNC server  protocal
 
lab --firefox (using socks 1080) to access internet        ok
 lab: firefox connect to lab:1080                    socks client protocal
 lab: 1080 redirect via ssh tunnel to mypc:10800    ssh tunnel
 mypc: 10800 is socks server                        socks server protocal
      putty decode socks request and redirect data to myhome via ssh tunnel
 
lab --firefox (using socks 10800) to access internet        fail
  lab: firefox connect to lab:10800                    socks client protocal
  lab: 10800 is redirected to lab:1080 via rinetd    rinitd tunnel
 lab: 1080 redirect via ssh tunnel to mypc:10800    ssh tunnel
 mypc: 10800 is socks server                        socks server protocal
      putty decode socks request and redirect data to myhome via ssh tunnel