Cisco VOIP behind Linksys NAT on cable modem

[oakleeman]

I recently purchased a used Cisco 12SP+ VOIP while I was still working for Network Operations at a university. The VOIP admin added my phone to the system so that I could "play" with trying to learn about VOIP. I tested the unit on campus and was able to place calls through the gateway and call other IP phones no problem. I brought the phone home and put it behind my Linksys BEFSR41 Cable Modem/DSL router. I was able to pull an IP from the router's DHCP server and access the VOIP server. Whenever I attempted to make a call through the gateway, I would call my cell phone. I wouldn't hear any ringing or sound through the IP phone, but my cell phone would ring and I could hear words from the IP phone on my cell phone. Whenever I called other IP phones, I could hear the phone dialing, but when someone answered they could hear me, but I could not hear them.

I don't work for NetOps anymore, but they have assured me that my phone is still in the system. I also recently upgraded the firmware on my router to 1.44.2. Now whenever I try to make gateway calls, the IP phone attempts to call and then just goes blank. Whenever I call other IP phones, I can hear it ringing, but still nothing on the other end.

I've tried putting the phone in the DMZ zone on my router as well as forwarding the ports that I noticed being used to the IP address of my IP phone. Does anybody have any hints or suggestions that would allow me to utilize this other that buying really expensive network equipment or getting multiple IPs at my house.

 

[tbilan]

This probably won't work. I think you'll need a version of NAT (Cisco) that is RTP/RTCP aware because the call control is done at a higher layer (probably session) which passes the IP address of the phone as part of the data to connect the call. This address is the non-NATted address. Unless their version of NAT can inspect and change the RTP/RTCP data stream it won't work. My friend had the same problem with a 7960.

You can use the Cisco softphone and have it use a URL to configure the IP address and it will work behind NAT.
Tom Bilan
TJBA, Inc.
CCNP, CCDA, MCSE, CNE, CCA, ASE

 

[oakleeman]

I currently have a DOTNET server running behind my router that I use for file sharing for my room-mates and for webhosting to the outside world. This server has 512MB of ram and dual nics. Could I put my server in place of the linksys router and have all of my traffic route through my server or would that still produce the same results? I know that it is a security risk, but I figure it might be worth a shot. Also, would doing this impede the speed of my network or any of the other 5-6 computers on my network.

 

[tbilan]

If it does skinny protocol translation then you'll be ok but my guess is it doesn't.

Here's something from Cisco's web page:

Verify Minimum Software Level for NAT on Cisco IOS Gateway / Routers
If using Network Address Translation, the minimum software level requirements must be met. Earlier versions of NAT do not support skinny protocol translation and will lead to one way voice issues.

The minimum software levels required for using NAT and skinny simultaneously are Cisco IOS® Software 12.1(5)T for IOS gateways to support skinny and H.323v2 with NAT. For more information, consult Nat-Support of IP Phone to Cisco CallManager

The minimum software level required for using NAT and skinny simultaneously on a PIX firewall is 6.0. For more information, consult Cisco Secure PIX? Firewall Version 6.0 Overview

Tom Bilan
TJBA, Inc.
CCNP, CCDP, MCSE & CNE

 

[oakleeman]

Well, I put my DOTNET server in as my router and configured NAT on it. The rest of the computers on my network don't seem to have a problem connecting, but still a problem with dialing. I have my firewall enabled on my public connection with port forwarding for the ports I know I'm needing. I haven't found where I can do a range of ports yet though like with my linksys. I noticed that some of the public ports don't get changed to something different with some of my outbound traffic....except for my phone of course. After that I got sidetracked messing with the windows media server on my server. I don't have VOIP working yet, but I do have an internet radio station going....lol. I'm an electrical engineer, not MIS, so I don't really understand what Skinny translation and stuff is or that much about Cisco IOS (I tried my hand at a UBR924 and couldn't get it to work). I'll just tinker with this here and there and try different stuff. If you have any hints or tips, let me know.

 

[tbilan]

I think you're screwed.

If I were doing it on a low budget I'd get a Cisco 1605R with at least 8MB of Flash and run the Cisco version of NAT that will fix the packets up as they leave the router. They ebay for about $200 but this is probably more than you want to spend just to play with the phone.
Tom Bilan
TJBA, Inc.
CCNP, CCDP, MCSE & CNE

 

[oakleeman]

Somewhere on my server I saw something about about specifying a H.323 gateway for telephony purposes. I don't know if it will work, but I'll toy with that idea.

My goal in all of this is to get my friends and family on a VOIP network where they can call each other without having to pay or use software and so that I can call my fiance without using up minutes on our cell phones. I wanted to go with Cisco because it was what I had access to plus NetOps had a gateway that I can use to make local calls (I don't have a land line at my house). If the Linksys VOIP router was able to receive phonecalls as well as send them out without having to pay to high of fee, that would be awesome. Do you know of a inexpensive hardware based alternative besides Cisco VOIP.

 

[tbilan]

I'm only experienced with Cisco products but I'm sure there are other options.

This phone is using Skinny protocol, not H.323. There are other phone protocols too like MGCP and SIP.

Also, you may want to look into SIP. Go to

http://www.cisco.com

and do a search on SIP.

I have several friends who use the Cisco Softphone and we play games at night while talking with IP telephony. It's pretty funny explaining to other people that we have a $20,000 rodger wilco network. I think VoIP technology is great as long as you have the quality of service to support the bandwidth and latency from end-to-end.
Tom Bilan
TJBA, Inc.
CCNP, CCDP, MCSE & CNE

 

[oakleeman]

Is softphone something that can be downloaded or does it have to be purchased? I've tried finding it in their download section and am not finding it. Think you can provide a URL for me?

 

[tbilan]

It's a purchase thing and if you have a CCO account it's out there for people to get updates.
Tom Bilan
TJBA, Inc.
CCNP, CCDP, MCSE & CNE