University blocking DC++
Blocking and Throttling
Many Universities have policies that limit the usage of peer to peer applications by students and employees. Typically, these policies block or limit the amount of bandwidth that p2p applications can use, and are enforced by employing solutions from Packeteer , NetLogic Microsystems , or a similar company. This software/hardware solution has the ability to look into a TCP packet, determine what class of application created it, then throttle or block it accordingly.
If you're behind such a block, please learn to live with it. Circumventing the block by proxying is detectable, is probably against your AUP, is technically difficult, and impossible to do without help from someone outside the firewall.
Network Address Translation
Other schools might have their network behind a NAT in which case an active connection is impossible. If you're inside a NAT, the IP reported by your computer will be in one of the non-routable IP ranges. In this case, try passive mode.
If you cannot connect to DC hubs or cannot transfer files in passive mode, the above advice about proxying applies.
A few schools use simple port blocking, where common ports used by DC++ and other p2p applications are blocked. DC++ uses a wide range of ports for outgoing traffic and incoming traffic by default. If the school blocks port 411 outgoing connections, then that effectively cuts you off from all DC hubs since that is the default hub port. Hub lists contain the full address of many hubs and those that run on non-standard ports (i.e. hub.example.com:1411) may work.
If you appear to be completely blocked from the DC network, the above advice applies.