On 4/29/2024 9:21 PM, Vladimir Oltean wrote:
On Mon, Apr 29, 2024 at 04:14:03PM -0400, Joseph Huang wrote:
How about the following syntax? I think it satisfies all the "not breaking
existing behavior" requirements (new option defaults to off, and missing
user space netlink attributes does not change the existing behavior):
mcast_flood off
all off
mcast_flood off mcast_flood_rfc4541 off
all off
mcast_flood off mcast_flood_rfc4541 on
224.0.0.X and ff02::1 on, the rest off
mcast_flood on
all on
mcast_flood on mcast_flood_rfc4541 off
all on (mcast_flood on overrides mcast_flood_rfc4541)
mcast_flood on mcast_flood_rfc4541 on
all on
mcast_flood_rfc4541 off
invalid (mcast_flood_rfc4541 is only valid if mcast_flood [on | off] is
specified first)
mcast_flood_rfc4541 on
invalid (mcast_flood_rfc4541 is only valid if mcast_flood [on | off] is
specified first)
A bridge port defaults to having BR_MCAST_FLOOD set - see new_nbp().
Netlink attributes are only there to _change_ the state of properties in
the kernel. They don't need to be specified by user space if there's
nothing to be changed. "Only valid if another netlink attribute comes
first" makes no sense. You can alter 2 bridge port flags as part of the
same netlink message, or as part of different netlink messages (sent
over sockets of other processes).
Think of mcast_flood_rfc4541 like a pet door if you will.
Ultimately, as far as I see it, both the OR-based and the AND-based UAPI
addition could be made to work in a way that's perhaps similarly backwards
compatible. It needs to be worked out with the bridge maintainers. Given
that I'm not doing great with my spare time, I will take a back seat on
that.
Nik, do you have any objection to the following proposal?
mcast_flood -> default/ off on
(existing flag) missing (specified/ (specified/
(on) nlmsg) nlmsg)
mcast_flood_rfc4541
(proposed new flag)
|
v
default/ flood all no flood flood all
missing
(off)
off flood all no flood flood all
(specified/nlmsg)
on flood all flood 4541 flood all
(specified/nlmsg) ^^^^^^^^^^
only behavior change
Basically the attributes are OR'ed together to form the final flooding
decision.
However, what I don't quite understand in your proposal is how many IPv4
addresses lie beyond the "224.0.0.X" notation? 256? Explain why there is
such a large discrepancy in the number of IPv4 addresses you are in
control of (256), vs only 1 IPv6 address with the new rfc4541 flag?
That's straight out of RFC-4541 ("coincidentally", these are also the IP
addresses for which the bridge will not create mdb's):
2.1.2.
2) Packets with a destination IP (DIP) address in the 224.0.0.X range
which are not IGMP must be forwarded on all ports.
This recommendation is based on the fact that many host systems do
not send Join IP multicast addresses in this range before sending
or listening to IP multicast packets. Furthermore, since the
224.0.0.X address range is defined as link-local (not to be
routed), it seems unnecessary to keep the state for each address
in this range. Additionally, some routers operate in the
224.0.0.X address range without issuing IGMP Joins, and these
applications would break if the switch were to prune them due to
not having seen a Join Group message from the router.
and
3.
In IPv6, the data forwarding rules are more straight forward because
MLD is mandated for addresses with scope 2 (link-scope) or greater.
The only exception is the address FF02::1 which is the all hosts
link-scope address for which MLD messages are never sent. Packets
with the all hosts link-scope address should be forwarded on all
ports.
