Linux – How to see multicast traffic from the same host

On Fedora 30, I'm trying to see multicast packets in another process on the same host. Using netstat, iperf, and tcpdump, I've verified that the group is joined and packets are sent to the multicast address, but the server-mode iperf never receives anything.

When I try this on another machine (CentOS 7) on a different network (that I didn't set up), I see the packets leave, but I don't see packets coming back but the server iperf does print out received packets. I'm guessing this is a kernel thing, but how to I enable this?

Here is some of the terminal session:

 jnordwick@jnkde ~ iperf -s -u -B 226.94.1.1 -i 1
------------------------------------------------------------
Server listening on UDP port 5001
Binding to local address 226.94.1.1
Joining multicast group  226.94.1.1
Receiving 1470 byte datagrams
UDP buffer size:  208 KByte (default)
------------------------------------------------------------

and the other terminal

 jnordwick@jnkde ~ netstat -g
IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      all-systems.mcast.net
eno1            1      226.94.1.1

now sending packets

 jnordwick@jnkde ~ iperf -c 226.94.1.1 -u -T 32 -t 3 -i 1
------------------------------------------------------------
Client connecting to 226.94.1.1, UDP port 5001
Sending 1470 byte datagrams, IPG target: 11215.21 us (kalman adjust)
Setting multicast TTL to 32
UDP buffer size:  208 KByte (default)
------------------------------------------------------------
[  3] local 192.168.2.155 port 47755 connected with 226.94.1.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec   131 KBytes  1.07 Mbits/sec
[  3]  1.0- 2.0 sec   128 KBytes  1.05 Mbits/sec
[  3]  0.0- 3.0 sec   385 KBytes  1.05 Mbits/sec
[  3] Sent 268 datagrams

Nothing appears in the server side perf, but if I run the exact same command on another network, I can see:

[jnordwick@network2 ~]$ iperf -s -u -B 226.94.1.1 -i 1
------------------------------------------------------------
Server listening on UDP port 5001
Binding to local address 226.94.1.1
Joining multicast group  226.94.1.1
Receiving 1470 byte datagrams
UDP buffer size:  208 KByte (default)
------------------------------------------------------------
[  3] local 226.94.1.1 port 5001 connected with 204.2.57.7 port 58971
[ ID] Interval       Transfer     Bandwidth        Jitter   Lost/Total Datagrams
[  3]  0.0- 1.0 sec   129 KBytes  1.06 Mbits/sec   0.000 ms    0/   90 (0%)
[  3]  1.0- 2.0 sec   128 KBytes  1.05 Mbits/sec   0.001 ms    0/   89 (0%)
[  3]  2.0- 3.0 sec   128 KBytes  1.05 Mbits/sec   0.001 ms    0/   89 (0%)
[  3]  0.0- 3.0 sec   385 KBytes  1.05 Mbits/sec   0.001 ms    0/  268 (0%)

tcpdump confirms the igmp joins and that packets are sent. I've dumped every interface possible (including the bonded and its slaves), and I can see the one interface the multicast packets leave from, but nothing comes back on any of them. I assume this is a kernel thing, since I don't think switches usually send multicast/broadcast traffic back to the sending host.