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

[David Woodhouse <dwmw2 infradead org>]

On Thu, 2009-09-10 at 13:03 -0700, Dan Williams wrote:
> On Thu, 2009-09-03 at 02:20 +0530, ritz wrote:
> > On Wed, 2009-09-02 at 15:46 +0100, David Woodhouse wrote:
> > > On Wed, 2009-09-02 at 13:30 +0530, ritz wrote:
> > > >   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 ?
> > > 
> > > For OpenConnect VPN connections you can set it with gconf-editor but I
> > > don't think it's exposed in the GUI.
> > > 
> > 
> > thanks, from what I was able to see, openconnect has an option "--mtu",
> > which vpnc lacks. This is set by vpnc helper script.
> 
> vpnc passes it from the concentrator to the client.

Does it? We added the $INTERNAL_IP4_MTU in vpnc-script solely for
openconnect, I thought -- it was making it up before, for vpnc.

> Does openconnect have that capability?  It's a really shitty VPN client
> that makes the user type in what's essentially (to the user) a random
> number.  This stuff should really be automatically determined, or
> pre-set by the admin.

Yes, openconnect negotiates it with the server. Most of the time the
user doesn't need to do anything at all.

But if your IT staff are stupid enough to filter ICMP and thus break
pMTU discovery, and if there's a link somewhere in your network which is
_smaller_ than the MTU on the VPN tunnel itself, then you'll find the
mtu option very useful.

You're right -- the better answer to ritz' question would have been "why
would you want to do that?".

-- 
dwmw2