On 22/10/2018 14.49, Rodney Baker wrote:
On Monday, 22 October 2018 23:10:54 ACDT Rodney Baker wrote:
[...]
224.0.0.1 is the "All hosts" multicast address - it is used by a router to address all hosts on the same network segment. This is used for host discovery. From https://www.tldp.org/HOWTO/Multicast-HOWTO-2.html;
"There are some special multicast groups, say "well known multicast groups", you should not use in your particular applications due the special purpose they are destined to:
- 224.0.0.1 is the all-hosts group. If you ping that group, all multicast capable hosts on the network should answer, as every multicast capable host must join that group at start-up on all it's multicast capable interfaces. - 224.0.0.2 is the all-routers group. All multicast routers must join that group on all it's multicast capable interfaces."
The full Ipv4 multicast address space registry is here; https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xht ml
Unless you are specifically wanting to receive multicast traffic (for example, to participate in dynamic routing protocols e.g. RIP, eigrp, ospf, bgp or is- is), or for receiving multicast video/audio traffic, you should not worry too much about it.
If you want it to work, you'll need to permit traffic to 224.0.0.0/24 on all your firewall interfaces where multicast-capable hosts exist.
The IPv6 equivalent addresses (link-local scope) are FF02::1 (for all hosts) and FF02::2 (for all routers). Node-local (or interface-local) equivalents are FF01::1 and FF01::2.
The full list of well-known multicast addresses for IPv6 are here: https:// www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast- addresses.xhtml
Just as a test, I tried to ping 224.0.0.1 on my local lan and got only one response - my L3 network switch which has igmp snooping enabled by default. No other devices responded.
I then enabled ip multicast-routing on my router and turned on PIM sparse-mode on the interface for my desktop vlan. Now, when I ping 224.0.0.1, both the router and the switch respond, but if I ping 224.0.0.2, only the router responds (as expected). They're the only 2 multicast-capable devices on the network.
[I turned multicast routing off again after the test as I have no need for it at home, although we do use it extensively at work.]
Thanks for the explanation :-) That rings a bell, because that router carries TV signal. And I have an application to watch TV that currently runs in a 42.3 machine. And the person that wrote it said that the TV module uses multicast. Indeed, the help forum for that application tells people that use an intermediate AP or router or switch that they need igmp snooping on. -- Cheers / Saludos, Carlos E. R. (from openSUSE 15.0 (Legolas))