I am running sip generating application on a linode to send sip traffic to linode another linode. It was running fine until I did a system-reboot. Now SIP packets are dropped with this error message (in syslog):

Feb 4 14:03:48 localhost kernel: nf_ct_sip: dropping packet: cannot parse SDP message IN= OUT= SRC=45.56.75.132 DST=178.79.176.71 LEN=560 TOS=0x00 PREC=0x00 TTL=64 ID=47781 DF PROTO=UDP SPT=5060 DPT=5060 LEN=540
UID=0 GID=0
Feb 4 14:03:48 localhost kernel: nf_ct_sip: dropping packet: cannot parse SDP message IN= OUT= SRC=45.56.75.132 DST=178.79.176.71 LEN=560 TOS=0x00 PREC=0x00 TTL=64 ID=47802 DF PROTO=UDP SPT=5060 DPT=5060 LEN=540
UID=0 GID=0
Feb 4 14:03:48 localhost kernel: nf_ct_sip: dropping packet: cannot parse SDP message IN= OUT= SRC=45.56.75.132 DST=178.79.176.71 LEN=560 TOS=0x00 PREC=0x00 TTL=64 ID=47803 DF PROTO=UDP SPT=5060 DPT=5060 LEN=540
UID=0 GID=0

Please use these steps to reproduce the problem:
- Create linode with ubuntu 14.04
- Install sipp :

apt-get update && apt-get install build-essential libpcap-dev libnet-dev libncurses-dev -y && wget https://github.com/SIPp/sipp/archive/v3.4.1.tar.gz && tar -xvzf v3.4.1.tar.gz && cd sipp-3.4.1
./configure && make
./sipp -sn uac 127.0.0.1

It will work (no packets dropped).

Then do a reboot from linode manager. Try to run sipp again.

ALL sip packets are dropped.

It seems that rebooting the server changes something in the kernel or the OS (not application specific).


I asked support, but the don't have answer.