On Thu, Jun 21, 2007 at 05:35:13PM +0200, Peter Rabbitson wrote: > Grant Taylor wrote: > > >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. should something like this work default proto static metric 5 nexthop via 58.173.108.1 dev vlan2 weight 10 nexthop via 10.20.20.106 dev ppp0 weight 20 and then let the dgd detect dead gateways and drop the relevant route about. > > I don't know about any working in-kernel solutions, but you can do it > trivially with netfilter and a cronjob: > > * In netfilter do this: > -t mangle -N ispA > -t mangle -A ispA -j RETURN > -t mangle -N ispB > -t mangle -A ispB -j RETURN > -t mangle -A PREROUTING -i $ifA -s ! a.a.a.a/aa -j ispA > -t mangle -A PREROUTING -i $ifB -s ! b.b.b.b/bb -j ispB > > where a.a.a.a and b.b.b.b are subnets describing your first 1 - 2 hops, > so traffic from your upstream router will not count. > > * Then make a cron job that run this every minute: > iptables -t mangle -vnxZL isp[AB] > and will look for the first number on the third line. If it is not 0 - > the link is alive, otherwise change the routing tables accordingly. > > Of course you can have up to 1 minute of downtime, but it does not look > so bad IMO. > > HTH > > Peter > _______________________________________________ > LARTC mailing list > LARTC@xxxxxxxxxxxxxxx > http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc >
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