Re: Equal-cost multipath question

From: Andi Kleen (
Date: Tue Aug 01 2000 - 09:58:11 EST

On Mon, Jul 31, 2000 at 02:49:25PM -0700, Ian Eure wrote:
> ** please cc to my address, since i'm not subscribed to the list.
> Hi there. I have a question regarding the behavior of equal-cost multipath
> in the 2.2.x kernel series.
> I'm trying to set up a system with >1 link to it's local network, in case
> of an ethernet adapter failure. I have three 3Com 905 NICs in the system,
> all with a different ip on the same subnet.

Make sure you use 3c59x driver, not the 3c90x driver from 3com.

> I start a ping to a host on the localnet. Works fine. I unplug the eth0
> interface, which those packets are going out of. Packets stop sending, and
> are not sent through any of the remaining interfaces.

Neighbour timeouts are currently not propagated to the routing code,
so it will only change on explicit interface down.

> It seems that ackets are be directed to the first route with the lowest
> metric. In the case of >1 route with the same metric, traffic is always
> sent to the first route. If this is the case, what it the point of even
> having ECMP?

Load balancing, and failover with routing daemons that support it (which
is currently none as far as I know, a few people were writing their own
primitive daemons to just check for nexthop alive)

> Perhaps I must use gated/zebra or some other routing daemon?

Yes, but probably only without automatic load balancing (because at least
zebra does not seem to support linux multipoint routes yet)


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