Dual Gateways

[Chris Gordon]

> On Fri, 2006-01-20 at 13:56 -0600, Mike McGrath wrote:
> > Aaron O'Hara wrote:
> > 
> > >Correct.
> > >
> > >If I statically put the gateway, my FC4 machine will 'load balance'
> > >between the two ISPs, but I don't want to have to statically insert the
> > >gateway or do a route add command.
> > >  
> > >
> > My understanding of having two default routes is that the first one will
> > always be used unless it is unavailable.  At which time it will fail to
> > the second route.  AFAIK simply having two routes doesn't load balances
> > between the two.  I think there are ways to do that but not just with
> > the route command.
> > 
> >     -Mike
> > 
> On Fri, 2006-01-20 at 12:13 -0800, Aaron O'Hara wrote:
> I am doing other stuff behind the scenes to take care of the load
> balancing, I just need the DHCP scripts to add the UG of BOTH ISPs
> instead of discarding one.  My other scripts take the info from the
> routing table and do the load balancing, but because there is no UG for
> one of the interfaces, it fails.

Can you explain a bit more what you are trying to do and what "behind
the scenes things you are doing?

"gateways" are also know as "default routes".  That is where the packet
DEFAULTS to if there is no specific route that matches the destination
of the packet.  There should be only one default location.  Haveing two
different default routes doesn't make sense -- it's not how things are
supposed to work.  Trying to have two default routes is only guaranteed
to not do what you want and at worst cause all sorts of asymetric
routing problems that will "break stuff"(tm).

If you want to connect to two different ISPs and route traffic
appropriately across those links, there are routing protocols designed
to handle that (RIP, BGP, OSPF, etc).  The zebra package provides
routing protocol capability.  Now the trick is that your ISP needs to
cooperate with you for you to use this and it's not something done on
DHCP type connections.

Again, it'd be helpful to know more of what you are trying to
accomplish, we may be able to provide a bit more help and guidance on
the right way to get it done.

Chris