mcast-proxy

About

This is a new daemon for OpenBSD that fills in a gap in the multicast
protocol support for network edges. More specifically we’re talking
about a multicast proxy.

The mcast-proxy is a less featured multicast routing daemon that is
mostly used on equipments that face client networks (end users). It is
mainly used when you don’t need a full multicast routing daemon (like
dvmrpd(8),
mrouted(8) or pim),
but you want to use your networks resources efficiently.
This implementation has the following features:

• Support IPv4 (IGMPv1/v2) multicast proxy
• Support IPv6 (MLDv1) multicast proxy
• Privilege dropping (runs as user)
• chroot jailing

The development of this daemon brought improvements to the IPv6
multicast stack, like:

• Initial MP support
  Now IPv6 multicast routing code uses the art routing table to store
  the multicast routes. This also means you can see your multicast
  routes in route(8).
• Support multiple rdomains
  The interfaces mif (multicast interface) are now domain specific, so
  you can have mif ids duplicated on different rdomains.
• Fixed a few problems in MLD code that prevented some client/server
  functionality

Notes

• The daemon is not yet pledge()d as there is no support for
  MRT(6)_* setsockopt() calls.
• IPv6 multicast proxy requires an OpenBSD -current, because of
  the recent kernel changes and netstat(1).

Running mcast-proxy

To run multicast routing protocols in your machines you have to configure
the following settings:

• Allow multicast routing:

    rcctl enable multicast

• Allow IGMP packets (IPv4 only):
  To allow IP options you have to configure your PF traffic pass rule to
  accept IP options. Example: change ‘pass’ to ‘pass allow-opts’.

• Add a multicast route (if the default doesn’t exist or is not correct)

    route add 224/8 192.168.0.1
    route add ff00::/8 fe80:baff2001%vio1

• In case you are using the default route for multicast you might need
  to specify an alternate multicast source. By default mcast-proxy only
  accepts multicast traffic from the same network of your interface.
  For example em0 has IPv6 address: 2001:100,
  but the multicast traffic comes from 2001:10. The same applies for IPv4.
  The mcast-proxy.conf:

    interface em0 {
        source 2001:/64
        upstream
    }

Design

The daemon code is split in the following file hierarchy:

• mcast-proxy.c: all IGMP/MLD related packet parsing
• mrt.c: the multicast routing table on userland
• kroute.c: all kernel interactions
• util.c: misc functions that did not fit the other files

Further Reading

• mcast-proxy.8
• mcast-proxy.conf.5
• License