netdev - [PATCH 1/6] Better documentation of mcast_to

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Message-Id: <20200412235038.377692-2-rouca@debian.org>
Date:   Mon, 13 Apr 2020 01:50:33 +0200
From:   roucaries.bastien@...il.com
To:     netdev@...r.kernel.org
Cc:     sergei.shtylyov@...entembedded.com,
        Stephen Hemminger <stephen@...workplumber.org>,
        Bastien Roucariès <rouca@...ian.org>
Subject: [PATCH 1/6] Better documentation of mcast_to_unicast option

From: Bastien Roucariès <rouca@...ian.org>

This option is useful for Wifi bridge but need some tweak.

Document it from kernel patches documentation

Signed-off-by: Bastien Roucariès <rouca@...ian.org>
---
 man/man8/bridge.8 | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/man/man8/bridge.8 b/man/man8/bridge.8
index b9bd6bc5..ff6f6f37 100644
--- a/man/man8/bridge.8
+++ b/man/man8/bridge.8
@@ -383,6 +383,32 @@ there is no MDB entry. By default this flag is on.
 Controls whether a given port will replicate packets using unicast
 instead of multicast. By default this flag is off.
 
+This is done by copying the packet per host and
+changing the multicast destination MAC to a unicast one accordingly.
+
+.BR mcast_to_unicast
+works on top of the multicast snooping feature of
+the bridge. Which means unicast copies are only delivered to hosts which
+are interested in it and signalized this via IGMP/MLD reports
+previously.
+
+This feature is intended for interface types which have a more reliable
+and/or efficient way to deliver unicast packets than broadcast ones
+(e.g. WiFi).
+
+However, it should only be enabled on interfaces where no IGMPv2/MLDv1
+report suppression takes place. IGMP/MLD report suppression issue is usually
+overcome by the network daemon (supplicant) enabling AP isolation and
+by that separating all STAs.
+
+Delivery of STA-to-STA IP mulitcast is made possible again by
+enabling and utilizing the bridge hairpin mode, which considers the
+incoming port as a potential outgoing port, too (see
+.B hairpin
+option).
+Hairpin mode is performed after multicast snooping, therefore leading to
+only deliver reports to STAs running a multicast router.
+
 .TP
 .BR "neigh_suppress on " or " neigh_suppress off "
 Controls whether neigh discovery (arp and nd) proxy and suppression is
-- 
2.25.1