Why did PPTP VPN stop working?

Question

linux

Hello.
There was a problem, the client stopped connecting to my pptpd server on centos 6.3.
In general, there is a remote server on it pptpd, everything worked, but at some point it simply stopped connecting.
this is what it says in the logs:
tail -f /var/log/messages

May 20 13:08:44 piskulina pptpd[29284]: CTRL: Client 5.189.13.x control connection started
May 20 13:08:45 piskulina pptpd[29284]: CTRL: Starting call (launching pppd, opening GRE)
May 20 13:08:45 piskulina pppd[29285]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.
May 20 13:08:45 piskulina pppd[29285]: pppd 2.4.5 started by jidckii, uid 0
May 20 13:08:45 piskulina pppd[29285]: Using interface ppp0
May 20 13:08:45 piskulina pppd[29285]: Connect: ppp0 <--> /dev/pts/4
May 20 13:08:45 piskulina pptpd[29284]: GRE: read(fd=7,buffer=60a400,len=8260) from network failed: status = -1 error = Protocol not available
May 20 13:08:45 piskulina pptpd[29284]: CTRL: GRE read or PTY write failed (gre,pty)=(7,6)
May 20 13:08:45 piskulina pppd[29285]: Modem hangup
May 20 13:08:45 piskulina pppd[29285]: Connection terminated.
May 20 13:08:46 piskulina pppd[29285]: Exit.
May 20 13:08:46 piskulina pptpd[29284]: CTRL: Client 5.189.13.x control connection finished

Nothing in iptables at all:

$ sudo iptables -t filter -L -n -v --line-numbers 
Chain INPUT (policy ACCEPT 10 packets, 728 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1      14M 5890M ISPMGR     all  --  *      *       0.0.0.0/0            0.0.0.0/0           
2     510K   66M ACCEPT     47   --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1     9257  566K TCPMSS     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x06/0x02 TCPMSS clamp to PMTU 
2     503K   45M ACCEPT     all  --  ppp+   eth0    0.0.0.0/0            0.0.0.0/0           
3     581K 1282M ACCEPT     all  --  eth0   ppp+    0.0.0.0/0            0.0.0.0/0           

Chain OUTPUT (policy ACCEPT 8 packets, 848 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1      19M 7928M ISPMGR     all  --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain ISPMGR (2 references)
num   pkts bytes target     prot opt in     out     source               destination

I won’t describe the config especially, since everything is according to the standard:

refuse-pap
refuse-chap
refuse-mschap
require-mschap-v2
require-mppe-128

Answer 1

Did it stop working after the update?
Alternatively, try manually loading the kernel module:

modprobe ip_nat_pptp
modprobe pptp
modprobe gre