On 06/21/07 17:35, Grant Taylor wrote:
The problem with this method is that I have yet to get it to start re-using the primary route when it becomes available again.
After doing some more testing and investigation, I think I know why the system appears to not be using the primary route. My test / lab setup consists of a Linux router with two subnets bound to one interface (eth0 and eth0:1) and my (VMWare) test Linux system with two ethernet interfaces bridged the the local LAN with one subnet on each interface. I have two (as far as Linux is concerned) physical interfaces so that I can have TX / RX counters for each interface to see which way the traffic is going out. This worked fine to have the system fall from the primary down to the secondary route when the primary route went away.
However I never saw the traffic from the test Linux system back to the interface for the primary route. After doing some investigation I think this is because the same MAC address is used for both the primary and secondary routes, seeing as how both addresses are on the same physical interface on my Linux router.
So, to test this, I took down the primary route, let the test Linux box fall back to the backup route, which it did. Then I brought the primary route back on line and waited. As expected the traffic did not start using the primary route, presumably because of MAC addresses for routes being cached with an association to a device. So, while the system was pinging out to the world with the primary route brought back up, I cleared entries from the local test Linux boxes ARP cache and all of the sudden, traffic started going out the correct interface.
So, now I think that the method of having two equal cost (metric) routes on the box will work. I'm now going to test where the two routes are different MAC addresses to see if the traffic does indeed start using the proper rout again (Seeing as how there should not be any confusion with MAC addresses.)
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