Windows 7 – Firewall issue with GNS3 routers


When I have connected my routers defined in GNS3 with a cloud pointing to my network card . HQ was able to access my LAN because it shares the same LAN .But in my Frame-Relay WAN , even if  I have all the networks in my routing table , it is impossible for a Branch location to ping something on the real network where you have Windows 7 or Windows Vista machines.

So after some reseach, I have found this interesting note:

Even if it is related to Windows Vista and even if you have some warning , it is applying this little patch. When , you apply under the DOS prompt the following command : netsh firewall set icmpsetting 8 enable . It will create depending on your topology  a new rule inside the Firewall “Networking – Echo Request(ICMPv4)”. This rule will be enabled.

In case if you want to revert your manipulation , as the command to revert back present in the previous document is not working , go then top the control center and find the previous created rule or rules and disabled it …

With this patch , you can enable your Windows 7 to icmp request.

Lab Date Booked

Hi ,

I booked my seat for the CCIE Voice Lab in Brussels for the 2th of  November of this year. So it is giving me around 7 months to study the exam…But will make an estimation/deadline  at the 15th July to see if I can stay the date as it is or not.

So now time to study , 31 weeks before the exam.

Routers and Voice Lab – Part 2

Yes Definitively , it will be difficult to have dedicated hardware so after more investigations , GNS3 is amazing and can do a bigger part of the job but need again to emulate this on the server so it is taking more resources. Take in mind that you can’t play with DSP so PRI connections and so on.

Think about 5 servers and a router Topology with at least 4 routers ( HQ, Branch 1, Branch 2, PSTN/CME). So it is becoming huge to maintain for hardware resources !!!

Routers and Voice Lab

Ok It is now time to start slowly on the lab again .

As It seems also clear that I will not have specific dedicated hardware , I will also try to push the discovery of GNS3 as we can already simulate a lot with this tool.

So tonight , I will investigate more in GNS3….

Motivation is still here and I will pass my exam before the end of year . Probably end of October or beginning of November .

Call Manager Services

Here is the list with all the Call Manager services:

  • Call Manager : Provides call processing
  • TFTP : responsible for building and serving files for devices
  • Messaging Interface : used with voice mail systems which use SMDI
  • IP Voice Media Streaming Application: provides functionality underlying MOH, conferences, MTP, …
  • Telephony Call Dispatcher (TCD) : provides hunting group with Auto-Attendant console
  • CTL Provider : works with CTL Client to change security mode from nonsecure to secure
  • MOH Audio Translator : it converts audio files for MOH utilisation
  • RIS Data Collector : collects and distributes real-time information
  • Extension Mobility : login/logout features
  • CDR Insert : is responsible for CDR operations
  • IPMA : Manager/assistant service
  • Extended functions : call-back and QRT service
  • Serviceability Reporter : generates reports on logged information
  • Webdialer : allows web application to make call control
  • CAPF : Issues locally Significant Certificates (LSC)

Real-Time Fax

Real-time fax over IP operates in a similar way of a regular fax transmission. The fax machines involved in the transmission synch up and then the fax data is sent between them over the intervening IP Network.

There are 2 methods of transporting fax in real time across the network:



When using fax-relay, the T30 fax signal from a connected fax machine is demodulated by the sending fax gateway and sent over the IP Network to a remote fax gateway. The remote fax gateway then recontructs the T30 fax signal and send it to the fax.

There are 2 types of fax-relay mechanisms:

Cisco fax-relay

T38 fax-relay

Cisco fax-relay is an older method. So a fax gateway terminates T30 fax tones from a local fax machine and then sends the fax data across an IP network by breaking the tones into HDLC frames and then transmitting them using RTP.

T38 fax-relay is the ITU standard T30 fax signal, it is demodulated at the local gateway and encapsulated into IP packets for transport over a network to a remote fax gateway which will then reconstruct the signal and play it to the fax. T38 includes also a mechanism by which a fax gateway can inform the remote gateway of its desire to change the media type from voice to data. T38 can also use TCP or UDP connections but will use more UDP.

For fax pass-through, modulated fax data is sent in-band across the IP network by a fax gateway using a voice codec (like G711 without any VAD or echo-cancellation). Also with fax pass-through, T30 fax calls are not distinguished from regular voice calls, they are simply sent in-band over the IP Network. With the fax detection tones, the gateway must be able then to switch to high-bandwidth codec. Fax pass-through is relatively bandwidth hungry and is sensitive to delay,jitter and packet loss

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