How can I know if IP Multicast is enabled
Solution 1
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?
Solution 2
On your linux box:
ip maddr show
gives:
@4Gtest ~]$ ip maddr show
1: lo
inet 224.0.0.1
inet6 ff02::1
2: p3p1
link 01:00:5e:00:00:01
link 33:33:00:00:00:01
link 33:33:ff:bd:7e:0f
link 01:00:5e:00:00:fb
link 01:00:5e:7f:ff:05
inet 224.127.255.5
inet 224.0.0.251
inet 224.0.0.1
inet6 ff02::1:ffbd:7e0f
inet6 ff02::1
Solution 3
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:29:F1:FF:EA
inet addr:78.46.74.27 Bcast:78.46.74.31 Mask:255.255.255.224
inet6 addr: fe80::20c:29ff:fef1:ffea/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5339836 errors:0 dropped:0 overruns:0 frame:0
TX packets:5486444 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:820300389 (782.2 MiB) TX bytes:1929979381 (1.7 GiB)
Base address:0x1400 Memory:e8820000-e8840000
Disable Multicast:
ifconfig eth0 -multicast
result:
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:29:F1:FF:EA
inet addr:78.46.74.27 Bcast:78.46.74.31 Mask:255.255.255.224
inet6 addr: fe80::20c:29ff:fef1:ffea/64 Scope:Link
UP BROADCAST MTU:1500 Metric:1
RX packets:5339836 errors:0 dropped:0 overruns:0 frame:0
TX packets:5486444 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:820300389 (782.2 MiB) TX bytes:1929979381 (1.7 GiB)
Base address:0x1400 Memory:e8820000-e8840000
No Multicast present in the interface
Enable Multicast :
ifconfig eth0 multicast
Solution 4
Using the ip
command one can check if an interface is multicast capable by:
ip link show eth0 | grep MULTICAST
To enable or disable multicast you can use:
sudo ip link set dev eth0 multicast [on|off]
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Mike Pennington
Updated on September 18, 2022Comments
-
Mike Pennington over 1 year
I have scripts that run IP multicast tests; however, my scripts are failing on a particular linux machine.
I know that I can look at
CONFIG_IP_MULTICAST
in the kernel configuration file to determine whether the kernel was compiled with this. However, it would be easier to flag missing requirements in my script if I could look at/proc
orsysctl
and get the answer.Is there a way to find if IP Multicast was compiled into the kernel without looking at
CONFIG_IP_MULTICAST
? -
Nils over 12 yearsBut how do you determine, if the router that box is connected to supports multicast?
-
Nikhil Mulley over 12 yearsMulticasting -- the sender sends a single datagram from its unicast address to the multicast group address and intermediary routers take care of making copies and sending them to all receivers that have joined the corresponding multicast group.
-
Nikhil Mulley over 12 yearsIf Yes, router needs to support the multicasting then. However, for senders/receivers it works on IGMP and for routers, its Protocol Independent Multicast (PIM). Router that supports PIM, usually enabled, and multicast group -- 224.0.0.0/4. Try putting up another pc listening in group at other end & send data to multicast group & check if receiver at the otherend receives data.Ify,router network does support multicasting.Few tools online: imj.ucsb.edu/mcast_detective (windows)
-
Mike Pennington over 11 yearsIt should be mentioned that
ifconfig
is now deprecated in linux... we should be using theiproute2
utilities. -
Askar over 9 yearsIt has been 2 years and we're still using
ifconfig
-
pevik over 7 years@oscar but that doesn't mean that it's good to do so as
ip
and other utilities from iproute2 are reflecting recent changes in Linux kernel networking code (unlikeifconfig
). -
A R over 6 yearsHow to add a muticast group to an interface?
-
Daniel Griscom about 4 yearsAnother five years...
ifconfig
still in my toolkit, but not sayin' it should be...