Re: [FFmpeg-devel] [PATCH v2] avformat: enable UDP IPv6 multicast interface selection - Rémi Denis-Courmont

From: "Rémi Denis-Courmont" <remi@remlab.net>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH v2] avformat: enable UDP IPv6 multicast interface selection
Date: Thu, 21 Mar 2024 09:26:15 +0200
Message-ID: <18F37B3F-99D8-4CDB-9197-A606C319E802@remlab.net> (raw)
In-Reply-To: <AS8P193MB1997CF4B7C2A82EA354CDCD48D332@AS8P193MB1997.EURP193.PROD.OUTLOOK.COM>

Le 20 mars 2024 14:35:28 GMT+02:00, "Ignjatović, Lazar (RS)" <Lazar.Ignjatovic@cubic.com> a écrit :
> Specifying egress interface is done by setting the setsockopt(IPV6_MULTICAST_IF) to the value of the interface, not address. On the other hand v4 for the similar option setsockopt(IP_MULTICAST_IF) sets it by definig an address (not interface). Without setting IPV6_MULTICAST_IF to the appropriate interface, default interface is chosen. We want to have control over this, and I cant se how this can be achieved without knowing the interface id.

>For ingress IPv6 traffic, the way to filter on which interface is being listened on is by binding to a mcast addres, which has sin6_scope_id properly set.

Your MR makes even less sense for multicast. For multicast there is no local address to match to an interface. So you just have to have the interface specified explicitly in addition to the LL group address. This is true for both egress and ingress.
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