batman-adv: mcast: detect, distribute and maintain multicast router presence
To be able to apply our group aware multicast optimizations to packets with a scope greater than link-local we need to not only keep track of multicast listeners but also multicast routers. With this patch a node detects the presence of multicast routers on its segment by checking if /proc/sys/net/ipv{4,6}/conf/<bat0|br0(bat)>/mc_forwarding is set for one thing. This option is enabled by multicast routing daemons and needed for the kernel's multicast routing tables to receive and route packets. For another thing if a bridge is configured on top of bat0 then the presence of an IPv6 multicast router behind this bridge is currently detected by checking for an IPv6 multicast "All Routers Address" (ff02::2). This should later be replaced by querying the bridge, which performs proper, RFC4286 compliant Multicast Router Discovery (our simplified approach includes more hosts than necessary, most notably not just multicast routers but also unicast ones and is not applicable for IPv4). If no multicast router is detected then this is signalized via the new BATADV_MCAST_WANT_NO_RTR4 and BATADV_MCAST_WANT_NO_RTR6 multicast tvlv flags. Signed-off-by:Linus Lüssing <linus.luessing@c0d3.blue> Signed-off-by:
Sven Eckelmann <sven@narfation.org> Signed-off-by:
Simon Wunderlich <sw@simonwunderlich.de>
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