Check out the sysctl? net.ipv4.conf.all.mc_forwarding

the other possible multicast parameters are

# sysctl -a | grep igmp net.ipv4.igmp_max_memberships = 20 # sysctl -a | grep mc net.ipv4.conf.pimreg.mc_forwarding = 1 net.ipv4.conf.ipsec0.mc_forwarding = 0 net.ipv4.conf.eth1.mc_forwarding = 1 net.ipv4.conf.eth0.mc_forwarding = net.ipv4.conf.lo.mc_forwarding = net.ipv4.conf.default.mc_forwarding = net.ipv4.conf.all.mc_forwarding = net.ipv4.neigh.pimreg.mcast_solicit = net.ipv4.neigh.ipsec0.mcast_solicit = net.ipv4.neigh.eth1.mcast_solicit = net.ipv4.neigh.eth0.mcast_solicit = net.ipv4.neigh.lo.mcast_solicit = net.ipv4.neigh.default.mcast_solicit = # sysctl -a | grep pim net.ipv4.conf.pimreg.arp_filter = net.ipv4.conf.pimreg.tag = net.ipv4.conf.pimreg.log_martians = net.ipv4.conf.pimreg.bootp_relay = net.ipv4.conf.pimreg.medium_id = net.ipv4.conf.pimreg.proxy_arp = net.ipv4.conf.pimreg.accept_source_route = net.ipv4.conf.pimreg.send_redirects = net.ipv4.conf.pimreg.rp_filter = net.ipv4.conf.pimreg.shared_media = net.ipv4.conf.pimreg.secure_redirects = net.ipv4.conf.pimreg.accept_redirects = net.ipv4.conf.pimreg.mc_forwarding = net.ipv4.conf.pimreg.forwarding = net.ipv4.neigh.pimreg.locktime = net.ipv4.neigh.pimreg.proxy_delay = net.ipv4.neigh.pimreg.anycast_delay = net.ipv4.neigh.pimreg.proxy_qlen = net.ipv4.neigh.pimreg.unres_qlen = net.ipv4.neigh.pimreg.gc_stale_time = net.ipv4.neigh.pimreg.delay_first_probe_time = net.ipv4.neigh.pimreg.base_reachable_time = net.ipv4.neigh.pimreg.retrans_time = net.ipv4.neigh.pimreg.app_solicit = net.ipv4.neigh.pimreg.ucast_solicit = net.ipv4.neigh.pimreg.mcast_solicit = 

More relevance:

It seems the most kernels(post v1) do support multicast by default or have CONFIG_IP_MULTICAST enabled while compiling. To check whether the compiled and running kernel subscribes to any multicast group, I would use netstat -g.

It seems the most kernels(post v1) do support multicast by default or have CONFIG_IP_MULTICAST enabled while compiling. To check whether the compiled and running kernel subscribes to any multicast group, I would use netstat -g.

# sysctl -a | grep igmp net.ipv4.igmp_max_memberships = 20 # sysctl -a | grep mc net.ipv4.conf.pimreg.mc_forwarding = 1   net.ipv4.conf.ipsec0.mc_forwarding = 0   net.ipv4.conf.eth1.mc_forwarding = 1   net.ipv4.conf.eth0.mc_forwarding = 1  net.ipv4.conf.lo.mc_forwarding = 0  net.ipv4.conf.default.mc_forwarding = 0  net.ipv4.conf.all.mc_forwarding = 1  net.ipv4.neigh.pimreg.mcast_solicit = 3  net.ipv4.neigh.ipsec0.mcast_solicit = 0  net.ipv4.neigh.eth1.mcast_solicit = 3  net.ipv4.neigh.eth0.mcast_solicit = 3  net.ipv4.neigh.lo.mcast_solicit = 3  net.ipv4.neigh.default.mcast_solicit = 3  # sysctl -a | grep pim net.ipv4.conf.pimreg.arp_filter = 0  net.ipv4.conf.pimreg.tag = 0  net.ipv4.conf.pimreg.log_martians = 0  net.ipv4.conf.pimreg.bootp_relay = 0  net.ipv4.conf.pimreg.medium_id = 0  net.ipv4.conf.pimreg.proxy_arp = 0  net.ipv4.conf.pimreg.accept_source_route = 1  net.ipv4.conf.pimreg.send_redirects = 1  net.ipv4.conf.pimreg.rp_filter = 0  net.ipv4.conf.pimreg.shared_media = 1  net.ipv4.conf.pimreg.secure_redirects = 1  net.ipv4.conf.pimreg.accept_redirects = 1  net.ipv4.conf.pimreg.mc_forwarding = 1  net.ipv4.conf.pimreg.forwarding = 1  net.ipv4.neigh.pimreg.locktime = 100  net.ipv4.neigh.pimreg.proxy_delay = 80  net.ipv4.neigh.pimreg.anycast_delay = 100  net.ipv4.neigh.pimreg.proxy_qlen = 64  net.ipv4.neigh.pimreg.unres_qlen = 3  net.ipv4.neigh.pimreg.gc_stale_time = 60  net.ipv4.neigh.pimreg.delay_first_probe_time = 5  net.ipv4.neigh.pimreg.base_reachable_time = 30  net.ipv4.neigh.pimreg.retrans_time = 100  net.ipv4.neigh.pimreg.app_solicit = 0  net.ipv4.neigh.pimreg.ucast_solicit = 3  net.ipv4.neigh.pimreg.mcast_solicit = 3 

# sysctl -a | grep igmp net.ipv4.igmp_max_memberships = 20 # sysctl -a | grep mc net.ipv4.conf.pimreg.mc_forwarding = 1  net.ipv4.conf.ipsec0.mc_forwarding = 0 net.ipv4.conf.eth1.mc_forwarding = 1 net.ipv4.conf.eth0.mc_forwarding = net.ipv4.conf.lo.mc_forwarding = net.ipv4.conf.default.mc_forwarding = net.ipv4.conf.all.mc_forwarding = net.ipv4.neigh.pimreg.mcast_solicit = net.ipv4.neigh.ipsec0.mcast_solicit = net.ipv4.neigh.eth1.mcast_solicit = net.ipv4.neigh.eth0.mcast_solicit = net.ipv4.neigh.lo.mcast_solicit = net.ipv4.neigh.default.mcast_solicit = # sysctl -a | grep pim net.ipv4.conf.pimreg.arp_filter = net.ipv4.conf.pimreg.tag = net.ipv4.conf.pimreg.log_martians = net.ipv4.conf.pimreg.bootp_relay = net.ipv4.conf.pimreg.medium_id = net.ipv4.conf.pimreg.proxy_arp = net.ipv4.conf.pimreg.accept_source_route = net.ipv4.conf.pimreg.send_redirects = net.ipv4.conf.pimreg.rp_filter = net.ipv4.conf.pimreg.shared_media = net.ipv4.conf.pimreg.secure_redirects = net.ipv4.conf.pimreg.accept_redirects = net.ipv4.conf.pimreg.mc_forwarding = net.ipv4.conf.pimreg.forwarding = net.ipv4.neigh.pimreg.locktime = net.ipv4.neigh.pimreg.proxy_delay = net.ipv4.neigh.pimreg.anycast_delay = net.ipv4.neigh.pimreg.proxy_qlen = net.ipv4.neigh.pimreg.unres_qlen = net.ipv4.neigh.pimreg.gc_stale_time = net.ipv4.neigh.pimreg.delay_first_probe_time = net.ipv4.neigh.pimreg.base_reachable_time = net.ipv4.neigh.pimreg.retrans_time = net.ipv4.neigh.pimreg.app_solicit = net.ipv4.neigh.pimreg.ucast_solicit = net.ipv4.neigh.pimreg.mcast_solicit =  

More relevance:

It seems the most kernels(post v1) do support multicast by default or have CONFIG_IP_MULTICAST enabled while compiling. To check whether the compiled and running kernel subscribes to any multicast group, I would use netstat -g.

It seems the most kernels(post v1) do support multicast by default.

[root@centos module]# grep CONFIG_IP_MULTICAST /usr/src/kernels/2.6.18-274.7.1.el5-i686/.config CONFIG_IP_MULTICAST=y [root@centos module]# netstat -g IPv6/IPv4 Group Memberships Interface  RefCnt Group --------------- ------ --------------------- lo 1 all-systems.mcast.net eth0 1 224.0.0.251 eth0 1 all-systems.mcast.net 

I see that eth0 interface on my host thinks its subscribed 224.0.0.251 basic mcast group . Also alternatively, if I ping the group or the network and then all the known multicast enabled host networks are returned to me, I would say multicast is working on the host. Can you try netstat -g or cat /proc/net/igmp and see if it returns any groups on your host?