I am trying to implement a wireless multicast ad-hoc network, but I don't know how it works.

I think I have to send my packets to a specific 224.0.0.* address, but I don't which one choose.

My network is and the packets are using the UDP protocol.

To which address should I send the packets ?

Do I have to configure something before ?

Which IP address my computers should have ? Do I need to change of network ?

  • 1
    Depending on what options your program use when sending your multicast packets, you may have to configure your host to choose which interface should be used by default for multicast.
    – BatchyX
    Jun 12, 2013 at 12:25

2 Answers 2


You don't configure multicast address anywhere.

Some box sends traffic out with multicast destination, this will automatically get L2 multicast address on the link.

This L2 multicast address is normally broadcasted in L2, unless there are some specific features enabled, like IGMP snooping to stop the flooding.

If IGMP snooping is enabled, then the L2 switch will learn which ports want to receive the multicast (they do IGMP join to the multicast group) and will not flood traffic to other than interested ports.

If L3 is involved, then you'll learn via PIM which ports are interested in receiving the multicast.

I can recommend this book for multicast basics, it's not JNPR specific.

If you don't know which addresses to use, if you have 2byte ASN, you should use GLOP block (with your ASN in it) if you don't have 2byte ASN your best bet is which can be thought has RFC1918 (e.g. for multicast.


Stay out out 224.0.0.x Those are all assigned for various specific purposes. As @ytti said, 239/8 is set aside for unspecified user purposes.

There's really nothing to configure. Multicast is a special case of broadcast traffic. Your ad-hoc wireless network is unlikely to know the difference.

One word of caution... most wireless chipsets are horrible at multicast. In an ad-hoc network, it's likely to be even worse as there's no AP to coordinate who can talk. There's was another recent NE question about slow multicast in wireless networks -- bottom line, broadcast (and thus multicast) traffic uses a common (to all radios) base channel which usually defaults to 1Mbps (yes one.)

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