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3 posts

Wannabe Geek

#156059 17-Nov-2014 23:11
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I am having trouble getting my VOIP back up and running after installing a CISCO ISR.

I got sick of my fritz box telling me what I was and was not allowed to do with my network so I got hold of a CISCO 800 Series integrated router. I have my fritz box in "internet connection sharing" mode, (which I assume is more or less a fancy way of saying bridge.) with the lan plugged into a lan port on my 800 Series, I am using the fritzbox for wireless and also as an ATA gateway for my phone.

I have internet all running no worries but cant get VOIP to work properly.

I can ring out but after a minute or two the phone will just go blank, I have been told it hangs up on the other end but just goes completely silent on my end, no one is able to ring in it just goes to answer phone after 15 secs silence.

I am almost 100% sure this is a porting issue as the 800 Series is NATing although I am a little confused as to why I can ring out but only for a minute or two. tho I am assuming this is something to do with re-registration during a call  ?

Currently I have my fritz statically assigned a ip address on my LAN Subnet and have port 5060 TCP and UPD forwarded to it but it is still not working I know that there are some RTSP ports involved but I am quite new to VOIP and am not really sure what they are, or if that is event the problem.

I would really appreciate any help from some VOIP Guru's.

Please refrain from telling me to put my fritz-box back on edge of network or telling me to get something else. this must be possible as is as the it more or less says in the fritzbox that "Internet Connection Sharing" is for this purpose.

Many thanks in advanced

PS. Im not a complete network noob so don't worrie to much about talking technical.

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597 posts

Ultimate Geek

  #1177690 17-Nov-2014 23:32
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Well since you said you're not a network noob I'm going to recommend you run some traces while placing a call to see what happens.

Which VoIP service are you using? Snap Plus I presume?

Here is a page of information which will help and explain a few issues with NAT and VoIP.

Stefan Andres Charsley


3 posts

Wannabe Geek

#1177696 18-Nov-2014 00:16
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Thanks for the reply.

Sorry I should have probably said not a complete networking noob lol.

since switches don't transmit out all ports is it possible to mirror the port on my 800 that my fritz is plugged into so that my pc can sniff the traffic? (this is were I am a little nooby).

as for my provider, yes I am snap vdsl with snap plus voip.

I have read allot about the issue with VOIP through NAT. the trouble is that I don't really know how to implement the work arounds 

I have been reading that cisco has some pass though stuff for SIP RTP and h323 I am really new to Cisco tho so don't understand the commands. 

from what I have read it seems that these are the ports that are needed.

SIP TCP/DUP 5060 - for registration? I have this forwarded to my fritz
RTP UDP 7078-7100 

Stuck as to how to implement this 

I think this sort of thing might be the answer but cant really make sense of it

Appreciate the help :)


597 posts

Ultimate Geek

  #1177698 18-Nov-2014 00:29
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I can't tell you the exact commands for Cisco.

You will need to learn how to Port forward then using the link I gave you, it will tell you all the ports you need to set up.

Frankly if you cannot setup the Cisco then you should place the fritz box as the edge device.

I don't know what you mean by "I got sick of my fritz box telling me what I was and was not allowed to do with my network".

I have never encountered a problem with fritz box restricting my network beyond its processing capabilities.

If you are adamant that you need the Cisco to be the edge device then you should learn the commands and the operating system.

Google helps. Here's a link for the 800 series and configuring VoIP.

Stefan Andres Charsley


3 posts

Wannabe Geek

  #1177699 18-Nov-2014 00:51
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Cool Thanks I will have a read of all that.

The fritzbox would not allow DHCP Relay and I need my Domain Controller to issue DHCP for various reasons, the biggest is that I need it to be the DNS server for correct domain functionality but fritzbox does not allow you to choose the DNS server it issues via DHCP

it also is very limited in its IPsec configuration so I was unable to configure it to match ISAKMP handshake from my other end point, there are a few other things that I have run into that made me want to biff it in the bin, but since my VOIP knowledge is very limited I have been stuck with it until now, I decided to ditch it and worrie about VOIP after lol (not my most wisest decision.)

in all they are meant to be a plug and play device that just doesn't have much room for custom network configurations

Hope fully I can get this going.

Thanks for your help.

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