Re: NM does not completely handle default route

[Robert Vogelgesang <vogel users sourceforge net>]

Hello,

On Sat, Oct 10, 2009 at 05:56:36PM -0400, Gene Czarcinski wrote:
> On Saturday 10 October 2009 17:32:42 Gene Czarcinski wrote:
> > OK, this is a followup to a lot of my previous email about NM handling the
> > default route when a system has multiple NICs.
> > 
> > I have closed out my BZ report for Fedora 11 as WONTFIX --
> > https://bugzilla.redhat.com/show_bug.cgi?id=523875 -- and have opened a new
> > report against rawhide --
> >  https://bugzilla.redhat.com/show_bug.cgi?id=528281
> > 
> > I do not expect that this problem will be fixed in time for F12 GA but hope
> > that it can be fixed post GA.
> > 
> > I have been poking around the NM source code mainly with grep and gedit.  I
> > believe it is possible/practical to fix things with any big re-write (which
> >  I believe is neither practical or desirable). [sure is a lot of code]  I
> >  mainly looked at how GATEWAYDEV=, GATEWAY=, and ONBOOT= (and their
> > ~/.gconf/system/networking/ counterparts) where handled.
> > 
> > Some characteristics/constraints --
> > 
> > 1.  Having a system with one or more NICs and no default route is a valid
> > configuration and should (must?) be supported by NM.

I think we should say MUST in this case.

> > 
> > 2. Regardless of having a default route or not, some connections should
> >  never be the default route (the intent, I believe, of the current
> >  implementation).

Agreed.

> > 
> > 3.  Having GATEWAYDEV=xxx in /etc/sysconfig/network will cause all NICs
> >  other than xxx to be marked as "never-default".  This is and should
> >  continue to be supported.

No.  As you noted in your bug #528281, system-config-network removes this
option, and I agree with that behaviour.  IMHO, GATEWAYDEV=xxx is an
old-time kludge, coming from times long ago where the networking init
scripts actually needed this option as a hint to get the default route
right.  The networking init scripts are now in a much better shape, and
we shouldn't commit ourselves to support this option forever.

GATEWAYDEV=xxx is not sufficient if you have three or more interfaces,
and only one of them should never get the default route.

> > 
> > 4. Only if a NIC is marked as NOT for all users can I mark it for
> >  "connection only" (never-default).  This needs to be fixed.  I should be
> >  able to mark a NIC which is available to all users (an ifcfg-xxx system
> >  configuration in /etc/sysconfig/network-scripts/) as a "connection only"
> >  (never-default) NIC.

Agreed.

> > 
> > 5.  I should be able to mark a NIC as the default route device.  I think
> >  this is needed for completeness but am not sure it is really required.

This would be overkill.  Either you specify your gateway in the config
file, or get it from DHCP.  If you have neither, you're lost, and such an
option wouldn't help in this case.

> > 
> > 6.  If two or more NICs with static IPs are configured with different
> >  default route, I do not care ... this is a mis-configuration.

This is a special case, but a valid configuration.  Sure, you can have
only one default route at a given time, but if you want to switch between
two or more uplinks, or two different environments that don't support
DHCP, such a setup can make your life more comfortable.

We just need clear semantics; "the most recently started interface
wins" would be fine, I guess.

> > 
> > 7.  The problem is not really with NICs that have static IPs but with those
> > that use dhcp where each dhcp server supplies a default route.

Agreed.

> 
> Oops ... I sent this partial message instead of saving the draft.  To continue 
> ...
> 
> 8. system-config-network currently has a problem with GATEWAYDEV=xxx being in 
> the /etc/sysconfig/network file and will delete it if you use s-c-n to change 
> the NIC system configuration files.  Any solution needs to avoid this problem.

As noted above, we don't actually need GATEWAYDEV=xxx, we need a way
to prevent some interfaces/connections from getting the default route,
and we only need this for connections that get their routes from DHCP
or some other peer, e. g. some VPN protocols.

What I specifically don't like about GATEWAYDEV=xxx is that it only allows
one single interface to get the default route.


> ---------------------------------------------
> What I propose is also something Dan mentioned ... add a new option/parameter 
> to the ifcfg-xxx file.  I tried adding "FOOBARBS=yes" to the file and this is 
> left alone by system-config-network and ignored by NM.  
> 
> So, I propose adding a new option/parameter such as "DEFAULTGW=yes|no" to the 
> system configuration file.

I think, a better name for this option would be "ALLOWDEFAULTROUTE=yes|no",
because this would clearly document what it really means, and it would be
obvious that you can set this option to "yes" for more than just one
interface/connection.

> 
> Upon loading the file (in ifcfg-rh/reader.c), if DEFAULTGW=no is specified, then 
> mark that connection as "never-default".
> 
> When saving the file (applying updates), if the connection is "never-default", 
> then set DEFAULTGW=no.  
> 
> A small problem occurs when I am changing a connection definition for "never-
> default" to allowing it for default.  For now, I propose that a connection 
> which is NOT "never-default" (that is, never-default is false in 
> ~/.gconf/...), then we should set DEFAULTGW=? for now.

And how is that any better than setting it to "yes" straight away?
Don't introduce too many special cases, please.

> 
> As an initial attempt at a fix, I think this may be "good enough".  Yes, having 
> DEFAULTGW=yes have some meaning may be useful but ... ???.  As described, I 
> think this will only involve ifcfg-rh/reader.c and ifcfg-rh/writer.c.
> 
> The patch to implement this should be fairly simple and I am going to give it 
> a try.
> 
> 
> Before I go too far on this ... any comments??

Please, don't name the new option "DEFAULTGW"; this would be confusing
for any experienced networking guy, because it is too similar to an
obvious name for an option that would actually specify the IP address
of the default gateway.  This name confuses yourself, because you are
not sure what DEFAULTGW=yes should mean.

This would be clearer if you think in terms of "ALLOWDEFAULTROUTE=yes",
because this would not imply that this interface/connection _must_ get
the default route, but is allowed to get it.


	Robert


> 
> Gene
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