Please disable CONFIG_IP_ROUTE_MULTIPATH_CACHED

[Tore Anderson]

Binary package hint: linux-source-2.6.20

After trying for long to figure out why my multipath routes didn't work (they behaved like singlepath routes), I finally was told on the netdev list that equal-cost multipath routes with caching is broken for forwarded packets, and that it will break multipath routes for such packets merely by being enabled (you don't even have to load the multipath_* modules).

Recompiling the kernel with CONFIG_IP_ROUTE_MULTIPATH_CACHED=n makes multipath routes work again, probably without caching but it's way better than nothing. So I request that you disable it in the default builds too until it's fixed upstream.

See the thread starting at <http://www.spinics.net/lists/netdev/msg26369.html>.

Tore

[Kyle McMartin (kyle)]

OK.

[Kyle McMartin (kyle)]

Datapoint for my reference: It's disabled in the Fedora kernels:
http://cvs.fedora.redhat.com/viewcvs/devel/kernel/configs/config-generic?rev=1.301&view=auto

[Tore Anderson (toreanderson)]

In linux-image-2.6.20-10-server_2.6.20-10.17_amd64.deb I find the following changelog entry:

  * Disable CONFIG_IP_ROUTE_MULTIPATH_CACHED
    - GIT-SHA 14dfd17d483d8466faf3605cf931c5f2fc7eac63
    - Bug ##90597

But:

tore@echo :) grep IP_ROUTE_MULTIPATH config-2.6.20-10-server
CONFIG_IP_ROUTE_MULTIPATH=y
CONFIG_IP_ROUTE_MULTIPATH_CACHED=y
CONFIG_IP_ROUTE_MULTIPATH_RR=m
CONFIG_IP_ROUTE_MULTIPATH_RANDOM=m
CONFIG_IP_ROUTE_MULTIPATH_WRANDOM=m
CONFIG_IP_ROUTE_MULTIPATH_DRR=m

Hmmm...?

Tore Anderson

[Tore Anderson (toreanderson)]

Yup. Disabling this is the right thing, that's for certain. In any case it'll soon go away.

http://www.spinics.net/lists/netdev/msg26628.html
http://www.spinics.net/lists/netdev/msg27014.html

Tore.