How To Check Multi-casting on Linux Client

carlosinfl · 07-02-2010, 10:03 AM

I have two machines connected to a generic Linksys switch and am running an application that requires multicasting be enabled on both clients on the switch. Is there a way I can test and or verify that both CentOS machines have multicast enabled on them?

gratuitous_arp · 07-02-2010, 08:32 PM

On one machine, enable responses to broadcast/multicast pings as root:

Code:

A-root# echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

On the other machine, ping the all-hosts multicast address:

Code:

B-user> ping 224.0.0.1
PING 224.0.0.1 (224.0.0.1) 56(84) bytes of data.
64 bytes from 192.168.0.2: icmp_seq=1 ttl=64 time=20.7 ms
64 bytes from 192.168.0.2: icmp_seq=2 ttl=64 time=41.6 ms
^C

You should receive a reply from the first machine. Enable it on both machines, and both should reply at the same time. The kernels must be configured for IP multicasting (CONFIG_IP_MULTICAST).