Multicast routing questions

Emeric POUPON emeric.poupon at
Thu Jun 25 16:18:44 UTC 2015

Ok thanks, I understand this case.
But the problem is that we perform a lot of unnecessary mforward calls from ip_input.

The mrt route cache lookup is performed thanks to the src/dst addresse couple.
The interface of the cached route does not match the current interface and that is what prevents "infinite" loops.

Is that really how it is meant to be done?


----- Mail original -----
De: "Andrey V. Elsukov" <bu7cher at>
À: "Emeric POUPON" <emeric.poupon at>, freebsd-net at
Envoyé: Jeudi 25 Juin 2015 07:48:44
Objet: Re: Multicast routing questions

On 24.06.2015 18:13, Emeric POUPON wrote:
> Hi,
> Actually, I don't really understand why imo.imo_multicast_loop is set
> to 1 in send_packet, ip_mroute.c
> It seems we don't need to loop the packet once it is mrouted? 

I think this can be used for the case, when on the router some app has
been joined to multicast group on the specific interface used as
outgoing in send_packet.

WBR, Andrey V. Elsukov

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