Hi,

we have a load balancer which is handling a lot of SIP traffic all day. There's always 20-40 Mbit SIP traffic going through. From time to time we see in our logs messages like these:

Sep 16 09:46:28 ecker /usr/sbin/kamailio[25505]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7f2d9d6b3ce0,1321,0,46.237.225.126:5060,16): Operation not permitted(1)
Sep 16 09:46:38 ecker /usr/sbin/kamailio[25194]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7efc982b8fc8,420,0,82.113.121.183:35794,16): Operation not permitted(1)
Sep 16 09:46:40 ecker /usr/sbin/kamailio[25505]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7f2d9d6b3ce0,1338,0,5.158.137.9:55067,16): Operation not permitted(1)
Sep 16 09:46:44 ecker /usr/sbin/kamailio[25183]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7efc982d9f48,450,0,178.165.131.197:37515,16): Operation not permitted(1)
Sep 16 09:46:49 ecker /usr/sbin/kamailio[25643]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7f93fb624530,496,0,172.56.7.69:25643,16): Operation not permitted(1)
Sep 16 09:46:55 ecker /usr/sbin/kamailio[25335]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7f41632cda98,598,0,80.215.234.139:3396,16): Operation not permitted(1)
Sep 16 09:46:56 ecker /usr/sbin/kamailio[25345]: ERROR: <core> [udp_server.c:591]: udp_send(): ERROR: udp_send: sendto(sock,0x7f41632f4840,459,0,94.197.120.191:8225,16): Operation not permitted(1)

I know that these messages can be produced by iptables blocking the outbound traffic. But our outbound chain looks basically like this:

root@ecker:~# iptables-save | grep OUTPUT
:OUTPUT DROP [0:0]
-A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-j ACCEPT
-A OUTPUT -m state --state INVALID -j DROP
-A OUTPUT -o lo -m state --state NEW -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
-A OUTPUT -m state --state NEW -j ACCEPT

We don't have the nf_ct_sip module loaded, syslog doesn't say anything, and even clearing all iptables rules doesn't eliminate those errors.

Has anyone ever seen this? It looks like a load thing, because at weekends there are significantly less errors.