(I know that what I'm wanting to do can be done, but for some reason I
can not get it to work for the life of me. I think I have been staring
at it too long and too closely.)
I have two different internet connections from two cooperating ISPs. I
also have a small 8 block of IPs that are globally routable that both
ISPs will route to me via my world facing globally routable IPs that I
have with them. I.e. ISP A has a route to 75.19.28.7/29 via 12.34.56.78
and ISP B has a route to 75.19.28.7/29 via 87.65.43.21.
I want to use one ISP as the primary default gateway and the other ISP
as a backup default gateway. That is to say I want to *NOT* use load
balancing rather just redundancy in this situation.
I do *NOT* need to use NAT because I do have the globally routable IP
address on *ALL* interfaces.
I.e.
eth0: 75.19.28.6 (DMZ)
eth1: 12.34.56.78 (ISP A)
eth2: 87.65.43.21 (ISP B)
I want this router to use the default gateway for ISP A of 12.34.56.254
and only use the default gateway of ISP B 78.65.43.1 if the default
gateway of ISP A can not be reached.
If I set up the interfaces with their IPs and subnets and set up
multiple default routes with varying metrics (for priority) and test by
taking an interface down, things work. However, this is not a realistic
test because the interface will never physically go down.
For the sake of discussion, let one link be a DSL modem and the other
link be a cable modem. Each of the links is an external modem that uses
an ethernet cable to connect in to the router. Thus no matter what the
state of the link coming in to my facility is, the link on the Linux
router will always be up b/c the ethernet between the router and the
modems sitting on the next shelf down will always be up.
I need a way for the Linux kernel to try to use a default gateway and
switch to another one if it does not see any traffic.
Any help that any one could offer will be greatly appreciated.
Thanks in advance,
Grant. . . .
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