14 | | Another related problem is that OpenVPN's components are not easily exchangable. This means that adding certain types of functionality (e.g. IPv6) or replacing current SSL and compression functionality is much more difficult than it needs to be. |
| 11 | Another related problem is that OpenVPN's components are not easily exchangable. This means adding certain types of functionality (e.g. IPv6) or replacing current SSL and compression functionality is much more difficult than it needs to be. As OpenVPN is essentially a special-case of a user-space network stack, it could be modularized so that the central core is implemented as a user-space network stack, and the other components such as VPN and routing would be modules in this stack. The above changes make it more straightforward to implement other protocols in the stack, such as IPv6. The network stack changes would also make it much more straightforward to implement alternative topologies for OpenVPN, such as full-mesh. The SSL and compression functionality should be modularized so that OpenVPN can be used with different SSL libraries or different compression algorithms. |
| 12 | |
| 13 | == Threading == |
| 14 | |
| 15 | Currently, OpenVPN is scaled on SMP machines by adding processes rather than threads. While it might be interesting to look into scaling OpenVPN across threads, there may be kernel-level bottlenecks that impede this, e.g. note the problems facebook had when trying to scale memcached, specifically the problems of having multiple threads contend for a single UDP socket: |
| 16 | * http://www.facebook.com/note.php?note_id=39391378919&ref=mf |
18 | | The current non-asynchrous-clean status of the event system makes maintenance of certain OpenVPN components quite tenuous, such as mtcp.c. It might be worthwhile to look into using libevent as the underlying i/o event system for OpenVPN (libevent is used by memcached). |
19 | | |
20 | | = Rethinking architecture for OpenVPN 3.0? = |
21 | | |
22 | | OpenVPN is essentially a special-case of a user-space network stack. In future development, OpenVPN could be modularized so that the central core is implemented as a user-space network stack, and the other components such as VPN and routing would be modules in this stack. The above changes make it more straightforward to implement other protocols in the stack, such as IPv6. The network stack changes would also make it much more straightforward to implement alternative topologies for OpenVPN, such as full-mesh. The SSL and compression functionality should be modularized so that OpenVPN can be used with different SSL libraries or different compression algorithms. The current i/o event system needs to be revamped into a true asynchronous model. While the current event model is partially asynchronous, it is not sufficiently clean to allow certain features to be implemented such as concurrent multithreading or the ability to listen on multiple interfaces simultaneously. |
23 | | |
24 | | |
25 | | * The current non-asynchrous-clean status of the event system makes maintenance of certain OpenVPN components quite tenuous, such as mtcp.c. |
26 | | * It might be worthwhile to look into using libevent as the underlying i/o event system for OpenVPN (libevent is used by memcached). |
| 20 | The current non-asynchrous-clean status of the event system makes maintenance of certain OpenVPN components quite tenuous, such as mtcp.c. While the current event model is partially asynchronous, it is not sufficiently clean to allow certain features to be implemented such as concurrent multithreading or the ability to listen on multiple interfaces simultaneously. To get these features the current i/o event system needs to be revamped into a true asynchronous model. It might be worthwhile to look into using libevent as the underlying i/o event system for OpenVPN (libevent is used by memcached). |