March 1, 2009

In the course of my CCIE studies, I’ve found the “Gatekeeper Address Resolution on ARQ” chart extremely useful.
Having a good understanding of the call-flow displayed the chart is key to understanding the debug gatekeeper main 10 and how the gatekeeper logically looks through configured parameters to decide how a call will be routed.

The chart (shown below) should be available in the CCIE Voice Lab exam. It can be found on Page 10-40 (pg 350 figure 10-14) in the CCM 4.1 SRND, which we’ve been told would be available in the lab.





Now back to the Hop-off Tech Prefix.
While there are many ways to route calls on a gatekeeper, we may need to use the Hop-off Tech-prefix configuration scenario in the lab if we’re specifically asked to do that, or if we’re instructed not to use the following:

 – Tech prefix
 – Default gw-type-prefix
 – E.164 Aliases (including Alias Static commands for CCM numbers)
 – Zone Prefix

Looking at the chart, we’ll need to match Step 1. Though it’s typically used to route calls to Remote Zones via a Location Request (LRQ), the gatekeeper can also generate an ACF at this stage if the Hop-off points to a Local Zone.

There isn’t much configuration needed to get this working; however, for your configuration to “stay working“, you would need to “hardcode” the signalling port used by your GK-Controlled Trunk (on Call Manager) to always use port 1720 as its Gateway Signalling Port.
This is quite important because CCM dynamically assigns port numbers for gateway signalling and for RAS.
These ports are set to 1720 and 1719 respectively on the gatekeeper by default.

If you don’t do this and the proctor resets your Trunks before grading (or maybe he/she even reboots the CCM box), then you’re screwed big-time 🙂

You can verify the Signalling and RAS ports CCM registered with on the gatekeeper with the show gatekeeper endpoints command:

GK-RTR#sh gatekeeper endpoints
CallSignalAddr  Port  RASSignalAddr   Port  Zone Name         Type    Flags
————— —– ————— —– ———         —-    —–    2789    4318  gk-zone1          VOIP-GW
    H323-ID: CCM_GKCT_1
    Voice Capacity Max.=  Avail.=  Current.= 0   1720   57634 gk-zone1          VOIP-GW
    H323-ID: CME_Trunk
    Voice Capacity Max.=  Avail.=  Current.= 0
Total number of active registrations = 2

As shown above, CME registers with 1720 by default, but CCM registers with 2789.
If CCM_GKCT trunk is reset, the port number would change to something totally different.
To configure CCM to use the port 1720 (signalling port) for a particular gatekeeper-controlled trunk through the CCM Service Parameters:

Navigate to the CCM Service Parameters and do a search for 1720. You’ll find the section under Clusterwide Parameters (Device – H323).
Change the name from None to the name of your trunk. In my case, my trunk is called CCM_GKCT.
Once this is done, you’ll notice that the port number for your CCM trunk would now be 1720 after you reset it.



We would now need to type in 3 commands to cater for the prefixes in HQ, BR1 and BR2.
 zone local gk-zone1
 gw-type-prefix 2* hopoff gk-zone1 gw ipaddr 1720
 gw-type-prefix 3* hopoff gk-zone1 gw ipaddr 1720
 gw-type-prefix 4* hopoff gk-zone1 gw ipaddr 1720
 no shutdown


Depending on whether we’ve been instructed to provide redundancy, we may need to include the secondary call-processing engine in the command for HQ and BR1 prefixes.
I’ve only got one call-manager running in my home lab, but here’s how you’ll configure it with two call-managers (assuming your second call-manager IP Address is

 gw-type-prefix 2* hopoff gk-zone1 gw ipaddr 1720 gw ipaddr 1720
 gw-type-prefix 3* hopoff gk-zone1 gw ipaddr 1720 gw ipaddr 1720


You can verify your configuration by using the show gatekeeper gw-type-prefix command (or by making calls ;-))


GK-RTR(config-gk)#do sh gatekeeper gw-type-prefix                         
Prefix: 2*    (Hopoff zone gk-zone1)
  Statically-configured gateways (not necessarily currently registered):
  Zone gk-zone1 master gateway list: CCM_GKCT_1

Prefix: 3*    (Hopoff zone gk-zone1)
  Statically-configured gateways (not necessarily currently registered):
  Zone gk-zone1 master gateway list: CCM_GKCT_1

Prefix: 4*    (Hopoff zone gk-zone1)
  Statically-configured gateways (not necessarily currently registered):
  Zone gk-zone1 master gateway list: CME_Trunk


PS: I’ve assumed your CME side has the following configuration:

dial-peer voice 1000 voip
 destination-pattern [23]…$
 session target ras
 incoming called-number .


Now, that’s a long post!!!!!

How it all began……..

February 18, 2009

It all started while I was a student @ Lagos State University, LASU as it was popularly called. I wasn’t satisfied with what school had to offer. Though I was in my 2nd year of a 5-year engineering course (Electronics & Computer Engineering) I just felt unfulfilled. I always believed the Uni couldn’t offer me what I wanted. I felt there was a bigger picture, and indeed there was!

I remember attending a Big Tent church meeting where Jacquie McCullough preached “No more abortions” and I knew I couldn’t even afford to drop out of school at that stage……there had to be another way!!!!

I started my IT journey with Microsoft 1999. Back in the days, folks were running NT 3.51 and NT 4.0. I passed my first Microsoft certification and got my MCP in October 2000.

Somewhere along the line I stumbled on serious networking (cos I don’t consider Microsoft as networking ;-)) and delved into CompTIA Network Plus in the year 2001.

Later in 2001, I came across CISCO and I said to myself this is it. Eight years later I’ve got CCNA, CCNP and CCVP under my belt.
I should have gone for the R & S CCIE a while ago, but I wasn’t motivated enough to even start to study for it.
Somewhere along the line I stumbled on Asterisk and Cisco voice and the rest is history.
I’m now working towards CCIE VOICE and would like to put my thoughts together and present it to the world to see. The CCIE journey has been quite exciting and challenging. Since I started my CCIE pursuit I’ve learnt so much; practically, I’ve learnt something new everyday. I’ve also learnt that I know so little, so little it could discourage, but I can’t let the passion die…….NEVER!!!!
The passion has brought me thus far in my love-affair with Cisco………..WELCOME TO MY BLOG!!!!!!