Re: Is it possible to set MTU for a vpn connection

[Dan Williams <dcbw redhat com>]

On Thu, 2009-09-03 at 02:31 +0530, ritz wrote:
> On Wed, 2009-09-02 at 10:56 -0400, Derek Atkins wrote:
> > ritz <khadgaray gmail com> writes:
> > 
> > > Hello
> > >
> > >   I do not see any option to set MTU under NMSettingVPN. All I could
> > > find was for ethernet, and wireless. Are there any plans to add this ?
> > 
> > The way I do this is manipulating the helper script to reset the MTU
> > after the VPN comes up.  It's a PITA.
> > 
> > > reference:
> > > http://live.gnome.org/NetworkManagerConfiguration
> > > http://bugzilla.gnome.org/show_bug.cgi?id=584200
> > 
> > -derek
> 
> 
> vpnc-console uses the the below to set MTU correctly
> 
>         if [ -n "$INTERNAL_IP4_MTU" ]; then

INTERNAL_IP4_MTU is pretty new I guess?  Must be added in 0.5.x I guess.
In any case, the patch below is about what should get used, yes.
Applied, thanks!

259259b5bbb5686ee6fc6bcf2a12eedd7192a905 (master)
a0a10c623063df4d2cd4bde56054c30b77d94ed9 (0.7.x)

Dan

>                 MTU=$INTERNAL_IP4_MTU
>         elif [ -n "$IPROUTE" ]; then
>                 DEV=$($IPROUTE route | grep ^default | sed 's/^.* dev
> \([[:alnum:]-]\+\).*$/\1/')
>                 MTU=$(($($IPROUTE link show "$DEV" | grep mtu | sed
> 's/^.* mtu \([[:digit:]]\+\).*$/\1/') - 88))
>         else
>                 MTU=1412
>         fi
> 
> 
> 
> Which would roughly translate to the below. It seems I would have to use
> libnl magic. Is there an alternate method ?
> 
> --- a/src/nm-vpnc-service-vpnc-helper.c
> +++ b/src/nm-vpnc-service-vpnc-helper.c
> @@ -368,10 +368,24 @@ main (int argc, char *argv[])
>         if (val)
>                 g_hash_table_insert (config,
> NM_VPN_PLUGIN_IP4_CONFIG_BANNER, val);
>  
> -       /* Set MTU to 1412 */
> -       val = uint_to_gvalue (1412);
> -       if (val)
> -               g_hash_table_insert (config,
> NM_VPN_PLUGIN_IP4_CONFIG_MTU, val);
> +       /* MTU */
> +       long int mtu ;
> +       char *tmp = getenv ("INTERNAL_IP4_MTU");
> +       if (tmp && strlen (tmp)) {
> +               errno = 0;
> +               mtu = strtol (tmp, NULL, 10);
> +               if (errno || mtu < 0 || mtu > 20000) {
> +                       nm_warning ("Ignoring invalid tunnel MTU '%s'",
> tmp);
> +                       mtu = 1412;
> +               }
> +       } else {
> +               // netlink magic to obtain mtu for default interface
> +               // and set vpnc-mtu = default-mtu - 88
> +               // if the above fails, set mtu = 1412
> +       }
> +       val = uint_to_gvalue ((guint32) mtu);
> +       g_hash_table_insert (config, NM_VPN_PLUGIN_IP4_CONFIG_MTU, val);
> +
>  
>         /* Send the config info to nm-vpnc-service */
>         send_ip4_config (connection, config);
> 
> 
>