netdev - Re: vrf and multicast is broken in some cases

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Date:   Wed, 15 Jan 2020 13:33:41 -0700
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>,
        Ben Greear <greearb@...delatech.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: vrf and multicast is broken in some cases

On 1/15/20 1:23 PM, Ido Schimmel wrote:
> 
> I'm not sure this is the correct way (David?). Can you try to delete
> this default route and instead add a default unreachable route with an
> high metric according to step 3 in Documentation/networking/vrf.txt:
> 
> "
> 3. Set the default route for the table (and hence default route for the VRF).
>        ip route add table 10 unreachable default metric 4278198272
> 
>    This high metric value ensures that the default unreachable route can
>    be overridden by a routing protocol suite.  FRRouting interprets
>    kernel metrics as a combined admin distance (upper byte) and priority
>    (lower 3 bytes).  Thus the above metric translates to [255/8192].
> "
> 
> If I'm reading ip_route_output_key_hash_rcu() correctly, then the error
> returned from fib_lookup() because of the unreachable route should allow
> you to route the packet via the requested interface.
> 

yes, IPv4 is a bit goofy with multicast (at least to me, but then I have
not done much with mcast).