PPTP VPN server not working.

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pault99
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Joined: 11 Apr 2017
Posts: 12

PostPosted: Sun Apr 12, 2020 13:20    Post subject: PPTP VPN server not working. Reply with quote
Hi all,

I have a Archer C9 v3 running on the very latest 42872 firmware.

I have never been able to get PPTP working on DD WRT with several firmware versions going back to sept 2019, until the latest version i upgraded to this week.

I had PPTP working way back in 2012 on a previous router with DD WRT, so was really hoping to get it working on this router. Yes i realise PPTP is weak, but its fine for the insecure application in hand.

So testing from several Windows 10 laptops i get the same issue.
Connects to IP ok, goes through authentication, and then fails about 20 seconds later.

Syslog from the router shows the following.


Apr 12 15:11:33 TaylorNet-DD-WRT daemon.info pptpd[18719]: CTRL: Starting call (launching pppd, opening GRE)
Apr 12 15:11:33 TaylorNet-DD-WRT daemon.notice pppd[18720]: pppd 2.4.8 started by root, uid 0
Apr 12 15:11:33 TaylorNet-DD-WRT daemon.debug pppd[18720]: using channel 11
Apr 12 15:11:33 TaylorNet-DD-WRT daemon.info pppd[18720]: Using interface ppp0
Apr 12 15:11:33 TaylorNet-DD-WRT daemon.notice pppd[18720]: Connect: ppp0 <--> /dev/pts/0
Apr 12 15:11:33 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:36 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:39 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:42 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:45 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:48 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:51 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:54 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:11:57 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:12:00 TaylorNet-DD-WRT daemon.debug pppd[18720]: sent [LCP ConfReq id=0x1 ]
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.warn pppd[18720]: LCP: timeout sending Config-Requests
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.notice pppd[18720]: Connection terminated.
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.notice pppd[18720]: Modem hangup
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.info pppd[18720]: Exit.
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.err pptpd[18719]: GRE: read(fd=6,buffer=26470,len=8196) from PTY failed: status = -1 error = I/O error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.err pptpd[18719]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
Apr 12 15:12:03 TaylorNet-DD-WRT daemon.debug pptpd[18719]: CTRL: Reaping child PPP[18720]


This seems to be the key>> timeout sending Config-Requests
Any thoughts ?.

Thanks in advance for any help.
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kernel-panic69
DD-WRT Guru


Joined: 08 May 2018
Posts: 6911
Location: Texas, USA

PostPosted: Sun Apr 12, 2020 14:02    Post subject: Reply with quote
Have you tried disabling the CVE mitigation option for VPN?
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pault99
DD-WRT Novice


Joined: 11 Apr 2017
Posts: 12

PostPosted: Sun Apr 12, 2020 14:14    Post subject: Reply with quote
kernel-panic69 wrote:
Have you tried disabling the CVE mitigation option for VPN?


Thank you for the reply.
Where can i find that ?
kernel-panic69
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Joined: 08 May 2018
Posts: 6911
Location: Texas, USA

PostPosted: Sun Apr 12, 2020 16:14    Post subject: Reply with quote
It's only visible when you enable OpenVPN server or client. I guess it does not apply to PPTP, sorry for that.
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Please DO NOT PM me with questions; Ask in the forum.

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pault99
DD-WRT Novice


Joined: 11 Apr 2017
Posts: 12

PostPosted: Sun Apr 12, 2020 17:45    Post subject: Reply with quote
kernel-panic69 wrote:
It's only visible when you enable OpenVPN server or client. I guess it does not apply to PPTP, sorry for that.


Ok, thanks.
Im going to Factory default it later tonight. Then manually re-enter all my specific config again. A bit of a pain as i have specific port forwarding for various ESX virtual machines. But ive got it all in my head so shouldnt take too long hopefully.
kernel-panic69
DD-WRT Guru


Joined: 08 May 2018
Posts: 6911
Location: Texas, USA

PostPosted: Sun Apr 12, 2020 17:51    Post subject: Reply with quote
Hopefully, it's not an issue tied to pppd or rp-pppoe. I know there have been reports of issues with PPPoE.
_________________
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pault99
DD-WRT Novice


Joined: 11 Apr 2017
Posts: 12

PostPosted: Fri Apr 17, 2020 21:25    Post subject: Reply with quote
Hi all,

So i have Factory defaulted my Archer C9 v3 running Build 42872
And manually reconfigured the router to suit my home environment again.

So again, using my laptop on a 4G hotspot, the PPTP VPN fails to connect.
The logs on the router show.
PTY read or GRE write failed

Now, if i try to connect to the VPN while still inside the LAN, it connects instantly!.
Which in a way is somewhat good news.

As a test i have Disabled PPTP passthrough and applied. Then re-enabled it again and applied.
Made no difference.

Very frustrating.
So possibly, it looks like the routers own firewall is stopping the incomming PPTP traffic.
pault99
DD-WRT Novice


Joined: 11 Apr 2017
Posts: 12

PostPosted: Sat Apr 18, 2020 19:41    Post subject: Reply with quote
Ok.. Ignore previous post, PPTP VPN is working fine in 42872.

I got my son to test it from his apartment. Hes on BT Fibre FTTP, and it connects perfectly.

But when i test myself using my phone as a WiFi hotspot it doesnt work. So possibly MTU problem.
Anyway, good news. Very Happy
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