Clarify --block-ipv6 intent and direction.

--block-ipv6 is a fairly special-purpose option, and only blocks packet
in the client->server direction.  This is implied by not ever mentioning
the other direction in the existing documentation, but not written down.

Make this explicit, avoid confusion.

Also, point why this option exist (avoid IPv6 leakage from dual-stacked
clients around IPv4-only VPN offerings).

Trac: #1351

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Richard Bonhomme <tincanteksup@gmail.com>
Message-Id: <20201225164214.22771-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21407.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/doc/man-sections/vpn-network-options.rst b/doc/man-sections/vpn-network-options.rst
index 2668278944db43bf23634dce0285b2c5a8796fef..029834aa459682bbcc9bbba0087e0ec8c12425fe 100644 (file)
--- a/doc/man-sections/vpn-network-options.rst
+++ b/doc/man-sections/vpn-network-options.rst
@@ -21,7 +21,8 @@ routing.
   For this option to make sense you actually have to route traffic to the
   tun interface. The following example config block would send all IPv6
   traffic to OpenVPN and answer all requests with no route to host,
-  effectively blocking IPv6.
+  effectively blocking IPv6 (to avoid IPv6 connections from dual-stacked
+  clients leaking around IPv4-only VPN services).
 
   **Client config**
     ::
@@ -38,6 +39,12 @@ routing.
        --push "redirect-gateway ipv6"
        --block-ipv6
 
+  Note: this option does not influence traffic sent from the server
+  towards the client (neither on the server nor on the client side).
+  This is not seen as necessary, as such traffic can be most easily
+  avoided by not configuring IPv6 on the server tun, or setting up a
+  server-side firewall rule.
+
 --dev device
   TUN/TAP virtual network device which can be :code:`tunX`, :code:`tapX`,
   :code:`null` or an arbitrary name string (:code:`X` can be omitted for