I am working on Ubuntu 16.04 xenial with the x86_64 Linux 4.4.0-83-generic kernel.I have a udp multicast sender sending udp datagrams to the multicast group 226.1.1.1:4096.Ifconfig indicates, that multicast is activated:wlp4s0    Link encap:Ethernet  HWaddr cc:b0:da:f6:cb:67        inet addr:192.168.178.29  Bcast:192.168.178.255  Mask:255.255.255.0      inet6 addr: fe80::77ba:cd68:4b4e:33f5/64 Scope:Link      inet6 addr: 2003:8c:2820:c00:2063:e748:b633:bdf0/64 Scope:Global      inet6 addr: 2003:8c:2820:c00:a12e:cdde:cd01:66da/64 Scope:Global      UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1      RX packets:5027967 errors:0 dropped:0 overruns:0 frame:0      TX packets:2605226 errors:0 dropped:0 overruns:0 carrier:0      collisions:0 txqueuelen:1000       RX bytes:7076352870 (7.0 GB)  TX bytes:523006066 (523.0 MB)Wireshark shows that udp multicast datagrams are being sent and clients are joining the multicast group (192.168.178.29 is the sender and 192.168.178.42 is the client/receiver).netstat -ng shows, that the multicast group 226.1.1.1 is active:IPv6/IPv4 Group MembershipsInterface       RefCnt Group--------------- ------ ---------------------lo              1      224.0.0.1enp3s0          1      224.0.0.1wlp4s0          1      226.1.1.1wlp4s0          3      224.0.0.251wlp4s0          1      224.0.0.1lo              1      ff02::1lo              1      ff01::1enp3s0          1      ff02::1enp3s0          1      ff01::1wlp4s0          5      ff02::fbwlp4s0          1      ff02::1:ff01:66dawlp4s0          1      ff02::1:ff33:bdf0wlp4s0          1      ff02::1:ff4e:33f5wlp4s0          1      ff02::1wlp4s0          1      ff01::1However, I am not able to receive any multicast datagrams on the client machines. Has someone encountered this behavior before ?EDIT:This is the tcpdump from the packet sent from the android device:Frame 29525: 67 bytes on wire (536 bits), 67 bytes captured (536 bits)IEEE 802.11 QoS Data, Flags: .......T    Type/Subtype: QoS Data (0x0028)    Frame Control Field: 0x8801    .000 0000 0011 0000 = Duration: 48 microseconds    Receiver address: AvmAudio_3f:23:27 (e0:28:6d:3f:23:27)    Destination address: Espressi_0e:ad:2b (a0:20:a6:0e:ad:2b)    Transmitter address: Motorola_e8:d7:73 (e4:90:7e:e8:d7:73)    Source address: Motorola_e8:d7:73 (e4:90:7e:e8:d7:73)    BSS Id: AvmAudio_3f:23:27 (e0:28:6d:3f:23:27)    STA address: Motorola_e8:d7:73 (e4:90:7e:e8:d7:73)    .... .... .... 0000 = Fragment number: 0    1001 1101 0100 .... = Sequence number: 2516    Qos Control: 0x0000Logical-Link ControlInternet Protocol Version 4, Src: 192.168.178.23, Dst: 192.168.178.42    0100 .... = Version: 4    .... 0101 = Header Length: 20 bytes (5)    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)        0000 00.. = Differentiated Services Codepoint: Default (0)        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)    Total Length: 33    Identification: 0x0000 (0)    Flags: 0x02 (Don't Fragment)    Fragment offset: 0    Time to live: 64    Protocol: UDP (17)    Header checksum: 0x5539 [validation disabled]    [Header checksum status: Unverified]    Source: 192.168.178.23    Destination: 192.168.178.42    [Source GeoIP: Unknown]    [Destination GeoIP: Unknown]User Datagram Protocol, Src Port: 5001, Dst Port: 4096Data (5 bytes)0000  68 65 6c 6c 69                                    helli  29526 16.625870      192.168.178.23        192.168.178.42        UDP      67     5001  4096 Len=5And this is from the linux machine to the client on 192.168.178.42:16809 9.575857       192.168.178.29        192.168.178.42        UDP      65     43981  4096 Len=3Frame 16809: 65 bytes on wire (520 bits), 65 bytes captured (520 bits)IEEE 802.11 QoS Data, Flags: .......T    Type/Subtype: QoS Data (0x0028)    Frame Control Field: 0x8801    .000 0000 0010 1100 = Duration: 44 microseconds    Receiver address: AvmAudio_3f:23:27 (e0:28:6d:3f:23:27)    Destination address: Espressi_0e:ad:2b (a0:20:a6:0e:ad:2b)    Transmitter address: LiteonTe_f6:cb:67 (cc:b0:da:f6:cb:67)    Source address: LiteonTe_f6:cb:67 (cc:b0:da:f6:cb:67)    BSS Id: AvmAudio_3f:23:27 (e0:28:6d:3f:23:27)    STA address: LiteonTe_f6:cb:67 (cc:b0:da:f6:cb:67)    .... .... .... 0000 = Fragment number: 0    0100 0111 1111 .... = Sequence number: 1151    Qos Control: 0x0000Logical-Link ControlInternet Protocol Version 4, Src: 192.168.178.29, Dst: 192.168.178.42    0100 .... = Version: 4    .... 0101 = Header Length: 20 bytes (5)    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)        0000 00.. = Differentiated Services Codepoint: Default (0)        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)    Total Length: 31    Identification: 0xbd2d (48429)    Flags: 0x02 (Don't Fragment)    Fragment offset: 0    Time to live: 64    Protocol: UDP (17)    Header checksum: 0x9807 [validation disabled]    [Header checksum status: Unverified]    Source: 192.168.178.29    Destination: 192.168.178.42    [Source GeoIP: Unknown]    [Destination GeoIP: Unknown]User Datagram Protocol, Src Port: 43981, Dst Port: 4096Data (3 bytes)0000  73 64 0a                                          sd.
UDP multicast datagrams not being sent to external clients
linux;ubuntu;networking;udp