netdev - Re: [PATCH v3 net-next] net: multipath routing: configurable seed

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Date:   Wed, 14 Apr 2021 10:33:38 +0300
From:   Pavel Balaev <mail@...d.so>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Cc:     christophe.jaillet@...adoo.fr, davem@...emloft.net,
        kuba@...nel.org, yoshfuji@...ux-ipv6.org, dsahern@...nel.org
Subject: Re: [PATCH v3 net-next] net: multipath routing: configurable seed

On Tue, Apr 13, 2021 at 08:28:52PM -0700, David Ahern wrote:
> On 4/13/21 4:55 AM, Balaev Pavel wrote:
> > Ability for a user to assign seed value to multipath route hashes.
> > Now kernel uses random seed value to prevent hash-flooding DoS attacks;
> > however, it disables some use cases, f.e:
> > 
> > +-------+        +------+        +--------+
> > |       |-eth0---| FW0  |---eth0-|        |
> > |       |        +------+        |        |
> > |  GW0  |ECMP                ECMP|  GW1   |
> > |       |        +------+        |        |
> > |       |-eth1---| FW1  |---eth1-|        |
> > +-------+        +------+        +--------+
> > 
> > In this use case, two ECMP routers balance traffic between
> > two firewalls. If some flow transmits a response over a different channel than request,
> > such flow will be dropped, because keep-state rules are created on
> > the other firewall.
> > 
> > This patch adds sysctl variable: net.ipv4.fib_multipath_hash_seed.
> > User can set the same seed value on GW0 and GW1 for traffic to be
> > mirror-balanced. By default, random value is used.
> > 
> > Signed-off-by: Balaev Pavel <balaevpa@...otecs.ru>
> > ---
> >  Documentation/networking/ip-sysctl.rst |  14 ++++
> >  include/net/flow_dissector.h           |   4 +
> >  include/net/netns/ipv4.h               |  20 +++++
> >  net/core/flow_dissector.c              |   9 +++
> >  net/ipv4/af_inet.c                     |   5 ++
> >  net/ipv4/route.c                       |  10 ++-
> >  net/ipv4/sysctl_net_ipv4.c             | 104 +++++++++++++++++++++++++
> >  7 files changed, 165 insertions(+), 1 deletion(-)
> > 
> 
> This should work the same for IPv6.
I wanted to add IPv6 support after IPv4 will be approved,
anyway no problem, will add IPv6 in next version 
> And please add test cases under tools/testing/selftests/net.
This feature cannot be tested whithin one host instance, becasue the same seed
will be used by default for all netns, so results will be the same
anyway, should I use QEMU for this tests?