Re: Default Gateway option

[Dan Williams <dcbw redhat com>]

On Wed, 2012-10-10 at 12:16 -0400, Jérôme Poulin wrote:
> On Wed, Oct 10, 2012 at 11:19 AM, Dan Williams <dcbw redhat com> wrote:
> >> When setting a manual IP on a connection, the way the dialog box is
> >> made, Network Manager allows a user to enter one gateway by IP,
> >> however, in a logicial ways, a gateway should be system-wide or at
> >> least connection-wide, not address specific.
> >
> > Gateways are (for the most part) subnet specific.  They do not need to
> > be, but that covers 90% of the use-cases.  We've been discussing
> > changing this recently to allow more complicated routing arrangements,
> > but these wouldn't be relevant for most users.
> 
> I though only routes were subnet specific, not gateways? We're really
> talking of "route of last resort", right? Multiple gateway would
> happen in an advanced router setup but not with something as simple as
> Network Manager. Am I right?
> 
> Of course I'm not talking of multiple gateways due to multiple
> connected interface, metric of the interface will make the route win
> and allow the user to switch connections at will.

For most cases, you're going to have a default gateway/router that is in
your prefix and thus usually in your broadcast domain.  eg if you have
192.168.1.50/24, your default gateway/router will be somewhere in
192.168.1.x.  That's because to even start communicating with
192.168.1.x, you need to ARP it to find out it's MAC address, and ARP
only works in broadcast domains.

The current editor dialog is structured so that if you delete the
192.168.1.50/24 address, the gateway associated with that subnet also
gets deleted, so you're not left with a setup where you still have eg
10.0.0.5/8 with a default gateway of 192.168.0.1.  That's going to fail
quite spectacularly unless you really mean that setup and have
additional routes.

Dan