Linux IPv4 Multicast question

Hi,

I am trying to add IPv4 multicast feature in openwrt distribution for
embedded (linux based).

Before that I want to test the basic linux multicast how it works.

I have 3 redhat linux machines which have 2.6.21. I see from make
menuconfig that the IP multicast is already enabled. In order to
simulate a simple multicast clients and server, what should I do and
how to see the traffic ?
(I mean how to configure IGMP router and how to configure IGMP clients
and see some basic traffic like PING and iperf working).

Your input would be valuable.

Thanks in advance !!

--Krish

krishkar99 writes:
> Hi,

> I am trying to add IPv4 multicast feature in openwrt distribution for
> embedded (linux based).

> Before that I want to test the basic linux multicast how it works.

> I have 3 redhat linux machines which have 2.6.21. I see from make
> menuconfig that the IP multicast is already enabled. In order to
> simulate a simple multicast clients and server, what should I do and
> how to see the traffic ?
> (I mean how to configure IGMP router and how to configure IGMP clients
> and see some basic traffic like PING and iperf working).

To get, ICMP replies from all hosts (GNU/Linux boxen) for a multicast
address, you need to set 'net.ipv4.icmp_echo_ignore_broadcasts' sysctl option
to 0. And then, you can ping 224.0.0.1 (all-hosts group) or 224.0.0.251
(all mDNS hosts group).

---->8---->8----
abbe@chateau:~$ ping -c3 224.0.0.1
PING 224.0.0.1 (224.0.0.1) 56(84) bytes of data.
64 bytes from 172.16.0.3: icmp_seq=1 ttl=64 time=0.061 ms
64 bytes from 172.16.0.2: icmp_seq=1 ttl=64 time=0.212 ms (DUP!)
64 bytes from 172.16.0.30: icmp_seq=1 ttl=64 time=0.919 ms (DUP!)
64 bytes from 172.16.0.3: icmp_seq=2 ttl=64 time=0.047 ms
64 bytes from 172.16.0.2: icmp_seq=2 ttl=64 time=0.177 ms (DUP!)
64 bytes from 172.16.0.30: icmp_seq=2 ttl=64 time=0.874 ms (DUP!)
64 bytes from 172.16.0.3: icmp_seq=3 ttl=64 time=0.045 ms

--- 224.0.0.1 ping statistics ---
3 packets transmitted, 3 received, +4 duplicates, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.045/0.333/0.919/0.361 ms
abbe@chateau:~$ ping -c3 224.0.0.251
PING 224.0.0.251 (224.0.0.251) 56(84) bytes of data.
64 bytes from 172.16.0.3: icmp_seq=1 ttl=64 time=0.060 ms
64 bytes from 172.16.0.2: icmp_seq=1 ttl=64 time=0.184 ms (DUP!)
64 bytes from 172.16.0.3: icmp_seq=2 ttl=64 time=0.047 ms
64 bytes from 172.16.0.2: icmp_seq=2 ttl=64 time=0.182 ms (DUP!)
64 bytes from 172.16.0.3: icmp_seq=3 ttl=64 time=0.046 ms

--- 224.0.0.251 ping statistics ---
3 packets transmitted, 3 received, +2 duplicates, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.046/0.103/0.184/0.066 ms
----8<----8<----

You should also checkout Avahi[1], an mDNS implementation.

References:
[1] - http://www.avahi.org/

HTH
Ashish
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