List Archive: gentoo-server
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Haim Ashkenazi wrote:
> I just came across this article:
> It seems that I was doing things the hard way (using iproute with
> metrics). the one thing I don't understand is how to prefer one route
> over the other (e.g. when one connection is faster).
I believe the author is counting on a total failure of eth0 to drop the
primary route. Once eth0 goes down that route is withdrawn from the
routing table leaving only the eth1 route. Linux without turning on IP:
advanced router in the kernel will use only one gateway. I assume it
uses the first one you config and once that disappears the second will
The problem is that eth0 will hardly every fail completely. The only
way it would is if it is directly connected to say a DSL device and the
device became unplugged. That would completely drop eth0 and then the
failover would happen. If only the connection upstream from the DSL
device went down then the Linux box would happily send data to the up
ether interface of the DSL, router, switch, etc.
It would also work if you're terminating connections directly into the
Linux box... using a ds-1 card or something like that. Again this
assumes that the connections fail totally. A ds-1 usually will, but in
offices you're sometimes handed ether which terminates on a switch. That
switch will be up, but the router or upstream connection has failed.
I can't find much on the /proc/sys/net/ipv4/route/gc_timeout setting,
but what I did find suggests that it only provides timing as to when the
route is dropped. It doesn't add anyway to monitor the connection.
It's an interesting little hack assuming I'm right about what he's doing
with it, but I wouldn't go around implementing it on most networks.
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