netdev - Re: [PATCH net-next 1/2] mlxsw: spectrum_router: Offload blackhole routes

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Date:   Fri, 8 Feb 2019 08:24:49 -0800
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...lanox.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        Alexander Petrovskiy <alexpe@...lanox.com>,
        mlxsw <mlxsw@...lanox.com>
Subject: Re: [PATCH net-next 1/2] mlxsw: spectrum_router: Offload blackhole
 routes

On 2/7/19 11:34 PM, Ido Schimmel wrote:
> 
> Yes. This patch configures the route itself to drop packets, but we can
> instead configure it as a remote route and configure the adjacency entry
> to drop packets.
> 
> If you later want to change X routes using this blackhole nexthop to a
> different one, then create the new one and tell the hardware to do the
> switch in a single operation. It will basically grep over all configured
> routes and do:
> 
> s/blackhole_adjacency_index/new_adjacency_index/
> s/black_ecmp_size/new_ecmp_size/
> 
> See RALEU in drivers/net/ethernet/mellanox/mlxsw/reg.h

Thanks for the reference.

> 
> I assume that user can't put blackhole and normal nexthops in the same
> group?
> 

I allow a nexthop group to reference a nexthop that is a blackhole, but
the group can only contain the one entry. That allows multipath routes
to toggle between a blackhole and a real spec.