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Re: [Openvpn-devel] Many to one TCP question


  • Subject: Re: [Openvpn-devel] Many to one TCP question
  • From: Lonnie Cumberland <lonnie@xxxxxxxxxx>
  • Date: Tue, 27 Apr 2004 17:13:43 -0500

Thanks for replying to my posting on this matter as I am still trying to get clear understanding as to the advantages/disadvantages of using TCP/UDP protocals.

My guess is that most things are done via TCP over the Internet and I seem to remember that there are supposed to be many problems with trying to use UDP over the Internet because of firewalls, bridges and the like, or something like that.

Also, is it true that you cannot bridge with UDP connections for road warriors with Windows (OpenVPN) machines wishing to connect to Linux (OpenVPN) machines and servers?

I could be totally off base here, but it UDP protos would work then I could go along that route instead for my project which needs to also scale to a (potentially maybe) very large number of road wariors.

Cheers,
Lonnie

James Yonan wrote:

Lonnie Cumberland <lonnie@xxxxxxxxxx> said:



Hello All,

Well, I've been away from the list for a little while and was wondering if someone could please bring me up to speed on the development of the "Many-to-One" TCP progress?

It is my understanding that in the OpenVPN 2.0 (early) Beta, that UDP connections can be established in a many to one TAP/TUN interface, but how about the TCP side?



TCP support for multiple-clients going through a single tun/tap interface is
probably not going to be here for a while unless someone sponsors the work. The problem is that it's difficult to scale, because TCP connections require
one socket per client, while UDP connections can use a single socket to talk
to any number of clients. Most OSes lack an efficient API for waiting on the
status of a large number of sockets. The one notable exception is Linux 2.6
which has the epoll API. Most application developers get around this
limitation by using multiple threads or processes, where each thread/process
waits on a single socket. But then you have the inefficiency of a large
number of threads/processes and the interprocess communication overhead
entailed by that.


James