Re: REQUEST: Network Interface Failover and multi-DNS resolution

[Mike Fedyk <mfedyk matchmail com>]

Carlos Rodrigues wrote:

> Putting them both in resolv.conf doesn't work, as the second one is 
> queried only when the first is down.
>
> Running a local DNS server is just plain ugly (and while I can do it 
> just fine, what I'm proposing is automating this stuff).
>
> Fixing the servers to know about each other just can't be done. Each 
> one of them is inside his respective LAN, which has NAT to the 
> outside. We could put a single server just above them but that would 
> miss the whole point of having the two networks separate (they are 
> supposed to be self contained).

You can have SOA records in each server that points to the other name 
server so that your resolver will know which server to contact for 
what.  It's just like how the root dns servers work.  They don't contain 
all of the records for all domains, only pointers, and the networks 
don't need to be interconnected for that and each is self-contained.

> Both interfaces use DHCP. But when I unplug the one from which the DNS 
> servers and default gateway were obtained, nothing changes. My point 
> is that the second interface should take over completely (the required 
> settings came through DHCP when it was activated). If the first 
> interface comes back, it puts things back to normal.

Sounds interesting.  File a bug and see what happens.

> > > This would be very useful for cases such as a laptop with wired and 
> > > wireless networking. The "wired" connection would be the primary 
> > > interface. The "wireless" connection would take over if the "wired" 
> > > one goes down (they may be different networks, e.g. we have a 
> > > totally open and untrusted wireless lan and our linux users can't 
> > > just unplug the cable and move around, they are forced to restart 
> > > the interfaces).
> >
> >
> >
> >     You can add 2/more default gateways. In this case linux uses 'Dead
> > Gateway Detection' - see http://www.ssi.bg/~ja/dgd-usage.txt for 
> > example.
> > I've never used two network interfaces with DHCP, so I've never tried
> > this trick with DHCP, but you can :)
> > ...
>
>
> Well, I didn't knew that. However my point is Fedora's (and other 
> distros) network scripts should do this (or could do this), possibly 
> with some configuration options in system-config-network (something 
> like  an "interface takeover" checkbox and another on an interface to 
> set it as primary). You can't just ask people to go around adding 
> routes and tweaking stuff by hand when some of them don't even know 
> what routes are... That will only make them complain about how it used 
> to work just fine in Windows, and I don't know about you but I just 
> hate to hear that. 

Yowza.  First of all, this functionality is mostly for routers and 
requires kernel patches (that sometimes break things) for some 
functionality.  I doubt that the fedora project wants to add that 
overhead for the small userbase it would allow them to have.

Second of all, this part of Linux isn't very well documented (both the 
userspace commands and kernel functionality) and is very spread out.  Do 
some research and you'll see what I'm talking about.

I say file a bug.  At least the request can be tracked, and possibly 
implemented when there is enough of a community around it.  Finding a 
router distribution where this functionality can help also.  Then lurk 
in their lists and read their archives.

Personally I'd like some of this functionality also, but there just 
isn't much of a community for this stuff yet and I haven't done any 
heavy lifting on finding a solution either but it's on my to do list.

Bottom line, if you don't file any bugs, this will *never* happen in 
fedora and if there isn't anyone with enough drive to do that, then 
that's a good thing.  It shows user interest.

Mike