Show Connected Multicasts

Jun 2017

To show if an interface is actively listening to any multicast streams, we can show this by using the netstat command: (netstat -ng)

netstat -ng
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 224.0.0.1
eth2 4 239.0.200.1
eth2 1 224.0.0.1
eth3 1 224.0.0.1
eth4 1 224.0.0.1
eth5 1 224.0.0.1
eth0 1 224.0.0.1
eth1 1 224.0.0.1
lo 1 ff02::1
eth2 1 ff02::1
eth3 1 ff02::1
eth4 1 ff02::1
eth5 1 ff02::1
eth0 1 ff02::1
eth1 1 ff02::1

This is a packager (v8) that I have setup a service on. That service is an ABR service containing four streams, so the line:
eth2 4 239.0.200.1
Is interesting to me, I can see that from address 239.0.200.1 (the MFEL multicast output) Interface 2 is connected to four multicasts.
Another tool we can use is ip maddr this gives more information.

1: lo
inet 224.0.0.1
inet6 ff02::1
2: eth2
link 01:00:5e:00:c8:01
link 33:33:00:00:00:01
link 01:00:5e:00:00:01
inet 239.0.200.1 users 4
inet 224.0.0.1
inet6 ff02::1
3: eth3
link 01:00:5e:00:00:01
inet 224.0.0.1
inet6 ff02::1
4: eth4
link 33:33:00:00:00:01
link 01:00:5e:00:00:01
inet 224.0.0.1
inet6 ff02::1
5: eth5
link 01:00:5e:00:00:01
inet 224.0.0.1
inet6 ff02::1
6: eth0
link 33:33:00:00:00:01
link 01:00:5e:00:00:01
inet 224.0.0.1
inet6 ff02::1
7: eth1
link 01:00:5e:00:00:01
inet 224.0.0.1
inet6 ff02::1

On interface 2, we can see the same information, but just formatted in a different way:
2: eth2

link 01:00:5e:00:c8:01
link 33:33:00:00:00:01
link 01:00:5e:00:00:01

inet 239.0.200.1 users 4

inet 224.0.0.1
inet6 ff02::1