Use a ping script, which pings some IP every minute or so. Ping can bind to a specific interface. Ping -c 1 -w 1 -I eth1 $SOME_IP Ping -c 1 -w 1 -I eth2 $SOME_IP Check for return values for those pings. Change your default routes based on the ping results. This is the basic idea. You can add many other things to this, more IPs, more counts, change time interval... (Better use IPs than domain names, so that DNS queries won't have problem) > -----Original Message----- > From: lartc-bounces@xxxxxxxxxxxxxxx [mailto:lartc-bounces@xxxxxxxxxxxxxxx] > On Behalf Of Grant Taylor > Sent: Thursday, June 21, 2007 3:06 PM > To: Mail List - Linux Advanced Routing and Traffic Control > Subject: Redundant internet connections. > > (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. . . . > _______________________________________________ > LARTC mailing list > LARTC@xxxxxxxxxxxxxxx > http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc _______________________________________________ LARTC mailing list LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
