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Cisco RV120W PPTP Re-writing source IP

Answered Question
Dec 22nd, 2011
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I have a VoIP application that I'm trying to run over the PPTP VPN tunnel on a RV120W router.


The system is a NEC SV8100 PBX communicating with the NEC soft phone (SP310).  The system uses SIP to set up the call and for other signaling information.  It uses RTP to transmit/receive the audio stream.


The problem I'm having is that there is no audio stream from the soft phone.  The SIP communication and the audio stream to the soft phone works fine.  The symptom is: from the soft phone, the remote party cannot hear you, but you can hear them.


I did a packet trace on the RV120W and found the following:


No.TimeSourceDest.ProtocolInfo
948

9.358957

192.168.1.252

192.168.1.52

RTP

PT=ITU-T G.711 PCMU, SSRC=0x7F1621CA, Seq=14361, Time=779040

949

9.359530

192.168.1.1

192.168.1.252

RTP

PT=ITU-T G.711 PCMU, SSRC=0xE943F2E7, Seq=19090, Time=3940936556





RTP



192.168.1.252 => NEC PBX

192.168.1.52  => Soft phone connected via PPTP

192.168.1.1   => RV120W


As you can see, the Source IP address is being changed from its original 192.168.1.52 to 192.168.1.1.  The NEC PBX is expecting the packet to be coming from the softphone, (192.168.1.52) not the RV120W (192.168.1.1).  As a result it ignores the RTP packet from the soft phone and does not relay it to the remote party.


Is there any reason why the RV120W is performing NAT on PPTP packets?  Can this be disabled somehow?


Any ideas will be helpful.


Thanks!


--

Joe Ripley

Correct Answer by Nechitaylo about 3 years 2 months ago

Choosing RV220 is the option.

 

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Joe Ripley Fri, 12/23/2011 - 09:00
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It looks like there was a similar issue on the RV220W that was fixed in firmware v1.0.2.4 of that model:


Specifically:


Fixed an issue in which enabling a PPTP server changed the port

forwarding Source IP Address to the LAN IP address of the router instead of

the IP address of the device that was used to access the service.


This is exactly the problem that I'm having with the RV120W.  Is this a known problem that will be fixed in the next firmware release?  Does anyone know the ETA for the next release of RV120W firmware?


Thanks!


--

Joe Ripley

jasbryan Fri, 12/23/2011 - 09:25
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Joe,


I don't see any open Cdets/bugs regarding the issue specified. I would call the SBSC @ 1-866-606-1866 and open a support case so we can start documenting your issue and verifying if this could possibly be a bug with the RV120.We would need some packet captures, syslogs, and any other trouble shooting steps you have completely. Once we have good documented case with replication of your issue and verified all this information we can get approval for escalation.


Jasbryan

Joe Ripley Fri, 12/23/2011 - 11:10
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Jasbryan,


Thanks for the information!  I've contacted your SBSC office and have started a case regarding this problem.  I will assemble as much data on the issue as I can and email it to your office.


Just for you reference, Cisco has assigned a case ID to this trouble.  If you need the specific case number, let me know.


--

Joe Ripley

Nechitaylo Sat, 01/14/2012 - 11:56
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Hi. I have the same issue with this router.

After enabling PPTP Server forwarded requests from Internet to internal services have internal IP address of the router as the source address.

Because of that doesn't work spam-filter on internal mail server for example.

Should I open a new case with Support team as Joe did?


I have latest firmware at the moment - 1.0.2.6


Thanks.

Joe Ripley Mon, 01/16/2012 - 08:29
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Alexey,


I doubt you need to open a new support case for  this... my existing case (#620173783) is registered with Cisco and I've  been in contact with several of their support engineers.  According to  them, the problems with enabling the PPTP server on the RV120W router is  a known bug.  They were able to reproduce the problem that I had  outlined in my initial post and are (hopefully) working to solve the  problem.


None of the people I've been in touch with  have been able to provide an ETA for a fix.  If you want, you can get a  refund for your defective router from Cisco.  I ended up using a RV220W  for my particular application... the PPTP server on that router does not  cause these extraneous NAT problems. 


Best of luck to you!


--

Joe Ripley

Juan Quiroz Fri, 06/20/2014 - 08:39
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Hello Joe,

having a similar issue like you, but with CiscoRV180 and with Avaya IP Office IP-PBX and Avaya softphone, How did you solve your problem, are you using cisco RV220W? or not, are your voip services working fine over PPTP?

Thanks for your help

Joe Ripley Fri, 06/20/2014 - 20:23
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Yes, I am using the RV220W for that particular application.  VoIP services work normally over the PPTP tunnel on the RV220W.

It is disappointing that Cisco has not resolved the problem with the RV120W... seems like a very trivial fix to me. 

Take care...

--

Joe Ripley

Te-Kai Liu Mon, 01/16/2012 - 10:36
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There is a beta firmware 1.0.3.x that fixed the issue you mentioned. You would have to call the support center to get the beta firmware through an escalation process.


Message was edited by: tekliu

It turned out that firmware 1.0.3.8 has not fixed the issue. So we will have to wait for the next firmware.  Sorry for the false optimism.

Nechitaylo Thu, 02/02/2012 - 06:42
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The issue still persists in 1.0.3.8 firmware.

So I'm discussing refund now with Cisco support.

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