bridge: mdb: Document the catchall MDB entries

Document the catchall MDB entries used to transmit IPv4 and IPv6
unregistered multicast packets.

In deployments where inter-subnet multicast forwarding is used, not all
the VTEPs in a tenant domain are members in all the broadcast domains.
It is therefore advantageous to transmit BULL (broadcast, unknown
unicast and link-local multicast) and unregistered IP multicast traffic
on different tunnels. If the same tunnel was used, a VTEP only
interested in IP multicast traffic would also pull all the BULL traffic
and drop it as it is not a member in the originating broadcast domain
[1].

[1] https://datatracker.ietf.org/doc/html/draft-ietf-bess-evpn-irb-mcast#section-2.6

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>

diff --git a/man/man8/bridge.8 b/man/man8/bridge.8
index 9753ce9e92b4c9e759acca3dd6eb988e85b31505..4006ad23ea745af8f5b313b2df590cfd8a1e3831 100644 (file)
--- a/man/man8/bridge.8
+++ b/man/man8/bridge.8
@@ -1013,6 +1013,12 @@ device creation will be used.
 device name of the outgoing interface for the VXLAN device to reach the remote
 VXLAN tunnel endpoint.
 
+.in -8
+The 0.0.0.0 and :: MDB entries are special catchall entries used to flood IPv4
+and IPv6 unregistered multicast packets, respectively. Therefore, when these
+entries are programmed, the catchall 00:00:00:00:00:00 FDB entry will only
+flood broadcast, unknown unicast and link-local multicast.
+
 .in -8
 .SS bridge mdb delete - delete a multicast group database entry
 This command removes an existing mdb entry.