When examining multicast configurations on Red Hat Linux, the /proc/net/igmp file provides crucial information about active multicast groups. Your output shows:

Idx Device    : Count Querier   Group    Users Timer    Reporter
1   lo        :     0      V3
                010000E0     1 0:00000000       0
2   eth0      :     3      V3
                010000E0     1 0:00000000       0

The presence of entries in /proc/net/igmp indicates multicast is enabled at the kernel level. Specifically:

• 010000E0 represents the multicast group 224.0.0.1 (all-hosts group)
• The V3 marker shows IGMP version 3 capability
• Your server is listening on both loopback (lo) and Ethernet (eth0) interfaces

To get a complete picture, check these additional commands:

# Check kernel multicast routing
cat /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

# Verify interface multicast flags
ip link show eth0 | grep MULTICAST

# Check active multicast routes
route -n | grep 224.0.0.0

For practical verification, use these tools:

# Sender (on one machine):
socat - UDP4-DATAGRAM:224.1.2.3:1234

# Receiver (on another machine):
socat UDP4-RECV:1234,ip-add-membership=224.1.2.3:eth0 -

If packets are received, multicast is fully operational on your network.

The group 010000E0 (224.0.0.1) is automatically joined by all IP hosts. This doesn't indicate specific application membership, but rather fundamental multicast support.

For custom application groups, you would see additional entries like:

EF000001     2 0:00000000       0  # Example: 239.0.0.1

To permanently enable multicast (if not already set):

# Add to /etc/sysctl.conf
net.ipv4.icmp_echo_ignore_broadcasts=0
net.ipv4.conf.all.mc_forwarding=1

# Reload settings
sysctl -p

# Sample IGMP output analysis
$ cat /proc/net/igmp
Idx Device    : Count Querier   Group    Users Timer    Reporter
1   lo        :     0      V3
                010000E0     1 0:00000000       0
2   eth0      :     3      V3
                010000E0     1 0:00000000       0

This output indicates:

• The system has multicasting enabled (V3 indicates IGMP version 3)
• Interface eth0 shows 3 multicast groups
• The group address 010000E0 translates to 224.0.0.1 (all-hosts group)

To thoroughly check multicast capability:

# Check kernel multicast routes
$ ip mroute show
# Verify interface flags
$ ip -d link show eth0 | grep MULTICAST
# Test socket-level multicast
$ python3 -c "import socket; print(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP)"

Persistent configuration via sysctl:

# /etc/sysctl.conf
net.ipv4.conf.all.mc_forwarding=1
net.ipv4.conf.default.mc_forwarding=1

Interface-level activation:

$ sudo ifconfig eth0 multicast
$ sudo route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0

Using socat for basic multicast testing:

# Receiver (terminal 1)
$ socat -u UDP4-RECV:1234,ip-add-membership=224.1.1.1:0.0.0.0 -

# Sender (terminal 2)
$ echo "multicast_test" | socat - UDP4-DATAGRAM:224.1.1.1:1234,range=224.0.0.0/4

• Firewall rules: Ensure iptables -A INPUT -d 224.0.0.0/4 -j ACCEPT
• Switch configuration: Verify IGMP snooping isn't blocking traffic
• Kernel modules: Check lsmod | grep igmp for required modules