Show Connected Multicasts

Jun 2017

This page discusses two tools. ngstat and ip
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:
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