OpenVPN Support Forum

Can someone explain why OpenVPN has two daemons listening by default?

The documentation says this is happening:

openvpn runs 2 daemons by default

- 1 for UDP on port 1194
- 1 for TCP on port 443

This makes no sense to me. If one instance can run only one at a time, why is the default to listen on both? Do you have any idea why? Is it because it’s prepared to do one or the other “out-of-the-box” so you don’t have to configure anything?

Thanks,
Reid K.

Hi Reid,

By default Access Server will have one daemon per listening protocol per CPU core. And by default it will listen on both TCP and UDP.

The reason for this: the VPN daemon "openvpn-openssl" is basically the same as the open source openvpn(8) software, and any instance can only do one protocol for the tunnel.

The reason for one per CPU core: the software prior to the 2.6.x release in January was single-threaded. 2.6 introduced a DCO (data channel offload) feature where the bulk of the work in the VPN tunnel (encryption and decryption of tunnel traffic) is offloaded to kernel space, via a kernel module. Openvpn 2.6 is still single threaded, but the data channel will be managed by the kernel, distributed among CPU cores according to load.

DCO is still in beta in Access Server.

Regards, rob0