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It is useful, yes; and posting diffs on the mailing list is not the way to
get them reviewed and approved.  If you can get this on gerrit it will get
a proper review, and I would certainly like to see something like this
incorporated.

On 21 July 2015 at 15:41, John Nielsen <lists at jnielsen.net> wrote:

> I may be in a small minority since I a) use VXLAN, b) don’t hate multicast
> and c) use linuxbridge instead of OVS. However I thought I’d share this
> patch in case I’m not alone.
>
> If you assume the use of multicast, VXLAN works quite nicely to isolate L2
> domains AND to prevent delivery of unwanted broadcast/unknown/multicast
> packets to VTEPs that don’t need them. However, the latter only holds up if
> each VXLAN VNI uses its own unique multicast group address. Currently, you
> have to either disable multicast (and use l2_population or similar) or use
> only a single group address for ALL VNIs (and force every single VTEP to
> receive every BUM packet from every network). For my usage, this patch
> seems simpler.
>
> Feedback is very welcome. In particular I’d like to know if anyone else
> finds this useful and if so, what (if any) changes might be required to get
> it committed. Thanks!
>
> JN
>
>
> commit 17c32a9ad07911f3b4148e96cbcae88720eef322
> Author: John Nielsen <john at jnielsen.net>
> Date:   Tue Jul 21 16:13:42 2015 -0600
>
>     Add a boolean option, vxlan_group_auto, which if enabled will compute
>     a unique multicast group address group for each VXLAN VNI. Since VNIs
>     are 24 bits, they map nicely to the 239.0.0.0/8 "site-local" multicast
>     range. Eight bits of the VNI are used for the second, third and fourth
>     octets (with 239 always as the first octet).
>
>     Using this option allows VTEPs to receive BUM datagrams via multicast,
>     but only for those VNIs in which they participate. In other words, it
> is
>     an alternative to the l2_population extension and driver for
> environments
>     where both multicast and linuxbridge are used.
>
>     If the option is True then multicast groups are computed as described
>     above. If the option is False then the previous behavior is used
>     (either a single multicast group is defined by vxlan_group or multicast
>     is disabled).
>
> diff --git a/etc/neutron/plugins/ml2/linuxbridge_agent.ini
> b/etc/neutron/plugins/ml2/linuxbridge_agent.ini
> index d1a01ba..03578ad 100644
> --- a/etc/neutron/plugins/ml2/linuxbridge_agent.ini
> +++ b/etc/neutron/plugins/ml2/linuxbridge_agent.ini
> @@ -25,6 +25,10 @@
>  # This group must be the same on all the agents.
>  # vxlan_group = 224.0.0.1
>  #
> +# (BoolOpt) Derive a unique 239.x.x.x multicast group for each vxlan VNI.
> +# If this option is true, the setting of vxlan_group is ignored.
> +# vxlan_group_auto = False
> +#
>  # (StrOpt) Local IP address to use for VXLAN endpoints (required)
>  # local_ip =
>  #
> diff --git
> a/neutron/plugins/ml2/drivers/linuxbridge/agent/common/config.py
> b/neutron/plugins/ml2/drivers/linuxbridge/agent/common/config.py
> index 6f15236..b4805d5 100644
> --- a/neutron/plugins/ml2/drivers/linuxbridge/agent/common/config.py
> +++ b/neutron/plugins/ml2/drivers/linuxbridge/agent/common/config.py
> @@ -31,6 +31,9 @@ vxlan_opts = [
>                 help=_("TOS for vxlan interface protocol packets.")),
>      cfg.StrOpt('vxlan_group', default=DEFAULT_VXLAN_GROUP,
>                 help=_("Multicast group for vxlan interface.")),
> +    cfg.BoolOpt('vxlan_group_auto', default=False,
> +                help=_("Derive a unique 239.x.x.x multicast group for
> each "
> +                       "vxlan VNI")),
>      cfg.IPOpt('local_ip', version=4,
>                help=_("Local IP address of the VXLAN endpoints.")),
>      cfg.BoolOpt('l2_population', default=False,
> diff --git
> a/neutron/plugins/ml2/drivers/linuxbridge/agent/linuxbridge_neutron_agent.py
> b/neutron/plugins/ml2/drivers/linuxbridge/agent/linuxbridge_neutron_agent.py
> index 61627eb..a0efde1 100644
> ---
> a/neutron/plugins/ml2/drivers/linuxbridge/agent/linuxbridge_neutron_agent.py
> +++
> b/neutron/plugins/ml2/drivers/linuxbridge/agent/linuxbridge_neutron_agent.py
> @@ -127,6 +127,14 @@ class LinuxBridgeManager(object):
>              LOG.warning(_LW("Invalid Segmentation ID: %s, will lead to "
>                              "incorrect vxlan device name"),
> segmentation_id)
>
> +    def get_vxlan_group(self, segmentation_id):
> +        if cfg.CONF.VXLAN.vxlan_group_auto:
> +            return ("239." +
> +                    str(segmentation_id >> 16) + "." +
> +                    str(segmentation_id >> 8 % 256) + "." +
> +                    str(segmentation_id % 256))
> +        return cfg.CONF.VXLAN.vxlan_group
> +
>      def get_all_neutron_bridges(self):
>          neutron_bridge_list = []
>          bridge_list = os.listdir(BRIDGE_FS)
> @@ -240,7 +248,7 @@ class LinuxBridgeManager(object):
>                         'segmentation_id': segmentation_id})
>              args = {'dev': self.local_int}
>              if self.vxlan_mode == lconst.VXLAN_MCAST:
> -                args['group'] = cfg.CONF.VXLAN.vxlan_group
> +                args['group'] = self.get_vxlan_group(segmentation_id)
>              if cfg.CONF.VXLAN.ttl:
>                  args['ttl'] = cfg.CONF.VXLAN.ttl
>              if cfg.CONF.VXLAN.tos:
> @@ -553,9 +561,10 @@ class LinuxBridgeManager(object):
>              self.delete_vxlan(test_iface)
>
>      def vxlan_mcast_supported(self):
> -        if not cfg.CONF.VXLAN.vxlan_group:
> +        if not (cfg.CONF.VXLAN.vxlan_group or
> cfg.CONF.VXLAN.vxlan_group_auto):
>              LOG.warning(_LW('VXLAN muticast group must be provided in '
> -                            'vxlan_group option to enable VXLAN MCAST
> mode'))
> +                            'vxlan_group option or vxlan_group_auto must '
> +                            'be True to enable VXLAN MCAST mode'))
>              return False
>          if not ip_lib.iproute_arg_supported(
>                  ['ip', 'link', 'add', 'type', 'vxlan'],
>
>
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