dhcp: Only use DHCP server port if explicitly configured

If a DHCP server is running on the same host it isn't necessary to
bind the server port and might even cause conflicts.

diff --git a/conf/plugins/dhcp.opt b/conf/plugins/dhcp.opt
index 6b337bc3478b09308a08d17abba235baa3745952..7c6d31c879cba0dfdc54ee69a0898fddc59a6430 100644 (file)
--- a/conf/plugins/dhcp.opt
+++ b/conf/plugins/dhcp.opt
@@ -15,6 +15,21 @@ charon.plugins.dhcp.identity_lease = no
 charon.plugins.dhcp.server = 255.255.255.255
        DHCP server unicast or broadcast IP address.
 
+charon.plugins.dhcp.use_server_port = no
+       Use the DHCP server port (67) as source port when a unicast server address
+       is configured.
+
+       Use the DHCP server port (67) as source port, instead of the DHCP client
+       port (68), when a unicast server address is configured and the plugin acts
+       as relay agent.  When replying in this mode the DHCP server will always send
+       packets to the DHCP server port and if no process binds that port an ICMP
+       port unreachables will be sent back, which might be problematic for some
+       DHCP servers.  To avoid that, enabling this option will cause the plugin to
+       bind the DHCP server port to send its requests when acting as relay agent.
+       This is not necessary if a DHCP server is already running on the same host
+       and might even cause conflicts (and since the server port is already bound,
+       ICMPs should not be an issue).
+
 charon.plugins.dhcp.interface
        Interface name the plugin uses for address allocation.
 

diff --git a/src/libcharon/plugins/dhcp/dhcp_socket.c b/src/libcharon/plugins/dhcp/dhcp_socket.c
index c26fcc9209146b75e4ca531bdb2efad4913fc919..1e208d094f79e295985df6c425dd959fe265c948 100644 (file)
--- a/src/libcharon/plugins/dhcp/dhcp_socket.c
+++ b/src/libcharon/plugins/dhcp/dhcp_socket.c
@@ -800,7 +800,10 @@ dhcp_socket_t *dhcp_socket_create()
                destroy(this);
                return NULL;
        }
-       if (!is_broadcast(this->dst))
+       if (!is_broadcast(this->dst) &&
+               lib->settings->get_bool(lib->settings,
+                                                               "%s.plugins.dhcp.use_server_port", FALSE,
+                                                               lib->ns))
        {
                /* when setting giaddr (which we do when we don't broadcast), the server
                 * should respond to the server port on that IP, according to RFC 2131,
@@ -808,7 +811,9 @@ dhcp_socket_t *dhcp_socket_create()
                 * kernel will respond with an ICMP port unreachable if there is no
                 * socket bound to that port, which might be problematic with certain
                 * DHCP servers.  instead of opening an additional socket, that we don't
-                * actually use, we can also just send our requests from port 67 */
+                * actually use, we can also just send our requests from port 67.
+                * we don't do this by default, as it might cause conflicts with DHCP
+                * servers running on the same host */
                src.sin_port = htons(DHCP_SERVER_PORT);
        }
        if (bind(this->send, (struct sockaddr*)&src, sizeof(src)) == -1)