The CCIE Data Center exam is finally upon us, and it looks like we're getting more testing dates than we were originally told to expect. Each of the 4 sites that currently tests the CCIE Storage (San Jose, Brussels, Sydney and Tokyo) each get one day per week to test the DC lab on. So on average, there should be about 4 DC seats per site per month, or roughly 16 seats available worldwide per month. Then, beginning in February, RTP gets the Wednesday slot, and since they are only open 2-3 Wednesdays per month (a strange but common day off there I suppose), we will see roughly 2-3 spots added for the DC lab beginning then. Finally, the very rough timeframe to ramp up on testing racks, and therefore add additional CCIE DC seats, is set to takeoff sometime around July according to sources.

Also, for anyone wanting to get a last minute testing date in even this week, the RTP site just went live a few hours ago with additional seats for this Saturday and Sunday (Dec 15-16). Jump online to book those seats, as they'll go quickly. Routing and Switching, Voice, Security and Service Provider are all open this weekend.


A voice lab rack usually utilizes dedicated piece of hardware to simulate PSTN switch. Commonly, you can find a Cisco router in this role, with a number of E1/T1 cards set to emulate ISDN network side. It perfectly suits the function, switching ISDN connections between the endpoints. Additionally, it is often required to have an “independent” PSTN phone connected to the PSTN switch, in order to represent “outside” dialing patterns - such as 911, 999, 411 1-800/900 numbers. The most obvious way to do this is to enable a CallManager Express on the PSTN router, and register either hardware IP Phone or any of IP Soft-phones (such as IP Blue or CIPC) with the CME system.

However, there is another way to accomplish the same goal using IOS functionality solely. It relies on the IP-to-IP gateway feature, called “RTP loopback” session target. It is intended to be used for VoIP call testing, but could be easily utilized to loopback incoming PSTN calls to themselves. Let’s say we want PSTN router to respond to incoming calls to an emergency number 911. Here is how a configuration would look like:

voice service voip
allow-connections h323 to h323
interface Loopback0
ip address
dial-peer voice 911 voip
destination-pattern 911
session target ipv4:
incoming called-number 999
tech-prefix 1#
dial-peer voice 1911 voip
destination-pattern 1#911
session target loopback:rtp
incoming called-number 1#911

The trick is that only IP-to-IP calls could be looped back. Because of that, we need to redirect the incoming PSTN call to the router itself first, in order to establish an incoming VoIP call leg.

While this approach permits VoIP call testing, it lacks one important feature, available with the “real” PSTN phone: placing calls from the PSTN phone to the in-rack phones. However, you can always use “csim start” command on the PSTN router to overcome this obstacle. Have fun!

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