Thank you Josh, you're starting to point me at the correct direction. Now I know just setting a port to Trunk or General mode is NOT enough.  I have to assign what kind of VLAN packets(i.e. which VLAN ID) are allowed to pass through.  To do such assignment, I have to take 2 steps. first, tell the "vlan database" to recognize a VLAN ID globally, second, tell that some specific port is allowed to pass-through packets with that specific VLAN ID. So, in order to pass VLAN packets with VLAN ID 18-25 unmodified(tagged packets in, tagged packets out) from port g7 to port g8, I have to do: console# configconsole(config)# vlan databaseconsole(config-vlan)# vlan 18-25console(config-vlan)# exit console(config)# interface ethernet g7console(config-if)# switchport mode generalconsole(config-if)# switchport general allowed vlan add 18-25 tagged and do this for g8 again. And, if I want all 48 ports to act like this, I have to write such commands 48 times right? Any shortcuts?       Some helpful links for me: [URL] 
I'd like to accomplish such a goal, make all 5448 switch ports acts like "trunk", that is, just like an entry level switch. Yes, I want all VLAN tags to pass through transparently. Let me explain it more clearly. If I want the ethernet packet to be forwarded to port 2 without any modification, that is, PC 2 will receive the packet with exactly the same packet bytes as PC1 sends. Currently, I want to configure all switch ports to act like this, but how to do this? Any one can tell me the most concise CLI commands to accomplish this? or, can it be done via web interface? I have to complain again about the poor manual, who talks about this concept and that concept again and again(so many ambiguous statements although the manual author does not realize it),  BUT does not explain them at packet-content level, so I'm totally at a loss. I've tried it from web interface. Simply set port 1 and 2 to Access mode or General mode does not work. Please help me out. Thank you in advance.   
PowerConnect 5448, How to make all physical ports trunk, and allow all VLAN 
tags to pass through transparently