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
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