[Openvpn-devel] man: Clarify IV_HWADDR

Message ID 20210709131330.140347-1-openvpn@sf.lists.topphemmelig.net
State Superseded
Headers show
Series
  • [Openvpn-devel] man: Clarify IV_HWADDR
Related show

Commit Message

David Sommerseth July 9, 2021, 1:13 p.m.
From: David Sommerseth <davids@openvpn.net>

The IV_HWADDR description was only partially correct, as there are more
implementations using other values than the MAC address of the default
gateway.

The intention of this value is to provide a unique identifier of the
client and on some platforms this is not possible to retrieve other than
to generate this information.

The 64 bytes limitation is an arbitrary value, it is not enforced by
OpenVPN 2.x.  But it was considered a good idea to at least have some
reasonable upper limit of how long this string can be, at least for
those implementing support for this information.

Signed-off-by: David Sommerseth <davids@openvpn.net>
---
 doc/man-sections/server-options.rst | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Comments

Gert Doering July 9, 2021, 1:41 p.m. | #1
Hi,

On Fri, Jul 09, 2021 at 03:13:30PM +0200, David Sommerseth wrote:
> From: David Sommerseth <davids@openvpn.net>
> 
> The IV_HWADDR description was only partially correct, as there are more
> implementations using other values than the MAC address of the default
> gateway.

Feature ACK, but this text is actually still factually wrong:

> +  :code:`IV_HWADDR=<string>`
> +        This is intended to be a unique and persistent ID of the client.
> +        The string value can be any readable ASCII string up to 64 bytes.
> +        OpenVPN 2.x and some other implementations use the MAC address of
> +        the client's default gateway. If this string is generated by the

It was never "the MAC address of the default gateway" (which would be
"the plastic router in the corner", and specifically depending on "which
network is this client in, right now?").

It is the MAC address of the *client* interface that is used to reach
the default gateway.


So maybe a better wording would be

"... use the MAC address of the client's interface used to reach the
default gateway."

(it's the client's interface MAC, not the gateway's MAC).

gert

Patch

diff --git a/doc/man-sections/server-options.rst b/doc/man-sections/server-options.rst
index 047f2270..b026ac7b 100644
--- a/doc/man-sections/server-options.rst
+++ b/doc/man-sections/server-options.rst
@@ -467,8 +467,13 @@  fast hardware. SSL/TLS authentication must be used in this mode.
   When ``--push-peer-info`` is enabled the additional information consists
   of the following data:
 
-  :code:`IV_HWADDR=<mac address>`
-        The MAC address of clients default gateway
+  :code:`IV_HWADDR=<string>`
+        This is intended to be a unique and persistent ID of the client.
+        The string value can be any readable ASCII string up to 64 bytes.
+        OpenVPN 2.x and some other implementations use the MAC address of
+        the client's default gateway. If this string is generated by the
+        client, it should be consistent and preserved across independent
+        session and preferably re-installations and upgrades.
 
   :code:`IV_SSL=<version string>`
         The ssl version used by the client, e.g.