Thanks for the response David, Heres output of netstat -s before and after my app data: I have advised management to upgrade the kernel, but we have too many custom drivers on this embedded system :-(. It would take way too long to get everything working again. cat /proc/sys/net/core/netdev_max_backlog = 300 set to 1000 also, with no effect tried setting device to eth0 in ip_mreq struct for IP_ADD_MEMBERSHIP sock option, no change to packet loss. output of netstat after startup and before tx of packets /flash/sbin/netstat -s Ip: 1199 total packets received 0 forwarded 0 incoming packets discarded 884 incoming packets delivered 666 requests sent out 316 reassemblies required 16 packets reassembled ok Icmp: 59 ICMP messages received 0 input ICMP message failed. ICMP input histogram: destination unreachable: 10 echo requests: 48 echo replies: 1 58 ICMP messages sent 0 ICMP messages failed ICMP output histogram: destination unreachable: 10 echo replies: 48 Tcp: 8 active connections openings 4 passive connection openings 0 failed connection attempts 0 connection resets received 4 connections established 747 segments received 535 segments send out 0 segments retransmited 0 bad segments received. 0 resets sent Udp: 54 packets received 10 packets to unknown port received. 0 packet receive errors 64 packets sent error parsing /proc/net/snmp: Success after data tx: /flash/sbin/netstat -s Ip: 5469 total packets received 0 forwarded 0 incoming packets discarded 5138 incoming packets delivered 4801 requests sent out 316 reassemblies required 16 packets reassembled ok Icmp: 140 ICMP messages received 0 input ICMP message failed. ICMP input histogram: destination unreachable: 10 echo requests: 129 echo replies: 1 139 ICMP messages sent 0 ICMP messages failed ICMP output histogram: destination unreachable: 10 echo replies: 129 Tcp: 8 active connections openings 4 passive connection openings 0 failed connection attempts 0 connection resets received 4 connections established 2925 segments received 3590 segments send out 0 segments retransmited 0 bad segments received. 0 resets sent Udp: 2040 packets received 10 packets to unknown port received. 0 packet receive errors 1057 packets sent error parsing /proc/net/snmp: Success /flash/sbin/netstat -g IPv4 Group Memberships Interface RefCnt Group --------------- ------ --------------------- lo 1 224.0.0.1 eth0 1 231.10.11.1 eth0 1 224.0.0.1 eth1 1 224.0.0.1 I am a bit slow and cant make much out of this output though. My app showed 7 messages lost. cat /proc/net/dev Inter-| Receive | face |bytes packets errs drop fifo frame compressed multicast| lo: 1136388 1049 0 0 0 0 0 0 eth0: 1432490 4333 0 0 0 0 0 1025 eth1: 526993 1113 0 0 0 0 0 73 tunl0: 0 0 0 0 0 0 0 0 This makes more sense to me, as I can see the multicast packets received on eth0. The multicast packets include my data + data from mrouted - To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html