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Standalone Debug Options
------------------------
--show-gateway args
(Standalone) Show current IPv4 and IPv6 default gateway and interface
towards the gateway (if the protocol in question is enabled).
Valid syntax:
::
--show-gateway
--show-gateway IPv6-target
For IPv6 this queries the route towards ::/128, or the specified IPv6
target address if passed as argument.
For IPv4 on Linux, Windows, MacOS and BSD it looks for a 0.0.0.0/0 route.
If there are more specific routes, the result will not always be matching
the route of the IPv4 packets to the VPN gateway.
Advanced Expert Options
-----------------------
These are options only required when special tweaking is needed, often
used when debugging or testing out special usage scenarios.
--hash-size args
Set the size of the real address hash table to ``r`` and the virtual
address table to ``v``.
Valid syntax:
::
hash-size r v
By default, both tables are sized at 256 buckets.
--bcast-buffers n
Allocate ``n`` buffers for broadcast datagrams (default :code:`256`).
--persist-local-ip
Preserve initially resolved local IP address and port number across
``SIGUSR1`` or ``--ping-restart`` restarts.
--persist-remote-ip
Preserve most recently authenticated remote IP address and port number
across :code:`SIGUSR1` or ``--ping-restart`` restarts.
--prng args
*(Advanced)* Change the PRNG (Pseudo-random number generator) parameters
Valid syntaxes:
::
prng alg
prng alg nsl
Changes the PRNG to use digest algorithm **alg** (default :code:`sha1`),
and set ``nsl`` (default :code:`16`) to the size in bytes of the nonce
secret length (between 16 and 64).
Set ``alg`` to :code:`none` to disable the PRNG and use the OpenSSL
RAND\_bytes function instead for all of OpenVPN's pseudo-random number
needs.
--rcvbuf size
Set the TCP/UDP socket receive buffer size. Defaults to operating system
default.
--shaper n
Limit bandwidth of outgoing tunnel data to ``n`` bytes per second on the
TCP/UDP port. Note that this will only work if mode is set to
:code:`p2p`. If you want to limit the bandwidth in both directions, use
this option on both peers.
OpenVPN uses the following algorithm to implement traffic shaping: Given
a shaper rate of ``n`` bytes per second, after a datagram write of ``b``
bytes is queued on the TCP/UDP port, wait a minimum of ``(b / n)``
seconds before queuing the next write.
It should be noted that OpenVPN supports multiple tunnels between the
same two peers, allowing you to construct full-speed and reduced
bandwidth tunnels at the same time, routing low-priority data such as
off-site backups over the reduced bandwidth tunnel, and other data over
the full-speed tunnel.
Also note that for low bandwidth tunnels (under 1000 bytes per second),
you should probably use lower MTU values as well (see above), otherwise
the packet latency will grow so large as to trigger timeouts in the TLS
layer and TCP connections running over the tunnel.
OpenVPN allows ``n`` to be between 100 bytes/sec and 100 Mbytes/sec.
--sndbuf size
Set the TCP/UDP socket send buffer size. Defaults to operating system
default.
--tcp-queue-limit n
Maximum number of output packets queued before TCP (default :code:`64`).
When OpenVPN is tunneling data from a TUN/TAP device to a remote client
over a TCP connection, it is possible that the TUN/TAP device might
produce data at a faster rate than the TCP connection can support. When
the number of output packets queued before sending to the TCP socket
reaches this limit for a given client connection, OpenVPN will start to
drop outgoing packets directed at this client.
--txqueuelen n
*(Linux only)* Set the TX queue length on the TUN/TAP interface.
Currently defaults to operating system default.
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