Re: [PATCH net] ipv6: omit traffic class when calculating flow hash

On Fri, Jun 01, 2018 at 09:19:29PM +0300, Ido Schimmel wrote:

On Fri, Jun 01, 2018 at 12:34:41PM +0200, Michal Kubecek wrote:

quoted

Some of the code paths calculating flow hash for IPv6 use flowlabel member
of struct flowi6 which, despite its name, encodes both flow label and
traffic class. If traffic class changes within a TCP connection (as e.g.
ssh does), ECMP route can switch between path. It's also incosistent with
other code paths where ip6_flowlabel() (returning only flow label) is used
to feed the key.

Use only flow label everywhere, including one place where hash key is set
using ip6_flowinfo().

Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
Fixes: f70ea018da06 ("net: Add functions to get skb->hash based on flow structures")
Signed-off-by: Michal Kubecek <redacted>

Please consider adding a test case to
tools/testing/selftests/net/fib_tests.sh

Personally, I tested the patch by looping over different values of 'tos'
for 'ip route get' and confirmed that the same nexthop is selected.

Thanks for the tip, I'll look into it next week.

Michal Kubecek