Cisco’s Virtual CUBE & Modern IOS Toll Fraud Security

Good Morning Web World!

I found myself with a little bit of time this morning and I thought I’d share a bit of my latest tinkering.

Those of you that have followed this blog for a while may remember my first post where I talked about pointing a CUBE through an ASA out to my ITSP, Flowroute. That post is located here for your reading pleasure.

While the software/hardware has changed with my setup the idea is basically the same. I still have a CUCM system (now 11.x) running with a phone (I’ve felt like being different lately so currently I’m using a retro 7985G as my endpoint (G in this case does not mean Gigabit)). I also have a firewall, a Cisco 5506-X (it was time for an upgrade from the 5505) and I do still have a CUBE. My previous CUBE was a 3825 and it worked wonderfully but the 3825 has long since outlived its relevance in today’s enterprise environments. In my stack of possibilities I also have a 2921 and while it is still a very powerful and valid router, it just seems too easy.

Simple and straight forward is great but only until you’ve done simple and straight forward, then it becomes time to mix it up.

To that end, my replacement CUBE is virtual. Yes, I said virtual. If you follow Cisco and their products, you may already know about the Cloud Services Router, the CSR1000V. The CSR1000V is a virtual router that runs on a VMWare ESXi host. It runs IOS XE though there is some Linux/Unix on the backend that makes it tick.


Virtual CUBE Show Commands



When I first heard that it was possible to turn a CSR1000V into a CUBE, I was skeptical. As I have worked through the configurations and witnessed it work, I must say I am impressed.  The configuration is the same as with any other IOS XE router with exception of the interface naming conventions. There are three (3) Gigabit Ethernet interfaces and they are named Gigabit Ethernet 1, Gigabit Ethernet 2 and Gigabit Ethernet 3.  The configuration in ESXi is shown below.

CSR1000V Interfaces Config

In my case, I created three (3) separate interfaces on my vSwitch and pointed them at three (3) separate VLANs in my infrastructure. You could bond/Port Channel these interfaces if you wanted too but you will still be limited by the throughput of your host’s uplink(s).

A few important things to note…

  • When you deploy the OVA file in ESXi you are given a choice of multiple router “sizes” i.e. memory and processor. I am using the smallest size which is one vCPU and 4GB of vRAM. Some of the larger installations require an additional license.
  • Keep in mind that I am testing this configuration in a controlled lab environment. I am not sure of scale-ability and if you read Cisco’s CUBE configuration guide, located here, you’ll see that the virtual CUBE does have several restrictions that may make it impractical for some organizations.
  • In my previous post, my 3825 CUBE was running 12.4 IOS which did not include Toll Fraud Prevention, starting in 15.x and moving through IOS XE you need to be mindful of TFP and what it means when you are trying to make/receive calls on a Cisco H.323 or SIP Gateway.

Let’s talk for a moment on Toll Fraud Prevention. As stated above, all modern IOS and IOS XE versions include Toll Fraud Prevention mechanisms and if you use a router, physical or virtual, for voice you need to be aware of them.

Voice Service Config



If you look at the configuration snippet above, you’ll see that in the voice service configuration there is a trusted IP Address list. That list contains the IPs of my ITSP and my CUCM. If I remove those IPs from the list, calls fail. If you are linking your CUBE or gateway to multiple CUCMs or other systems you’ll want to have those IPs in that list as well. What this list does is let the good/known IPs in to complete transactions/calls on the gateway/CUBE and keeps the unknown/bad IPs out to prevent them from placing calls on the system. If you’ve ever set up an IP PBX on internet, you know that Toll Fraud is a real and serious threat. If you don’t want or need this feature you can also turn it off by entering “no ip address trusted authenticate” in your voice service configuration. This is not a recommended configuration but in your environment the TFP mechanisms may do more harm than good.

Thanks for reading, I hope this has been informative.


Configuration Example: Cisco CUBE with FlowRoute

So you’ve decided to step-up and get a “Big Boy” phone system. You’re done with CME and you’ve moved to Call Manager (Cisco can call it whatever it wants, but to many of us it will always be Call Manager). But wait, there is a problem… Call Manager won’t natively peer to your ITSP, so what do you do? While there may be many solutions, the best one that I have found involves using Cisco’s Unified Border Element or CUBE. CUBE, for those of you new to Cisco voice technology is a fancy term for a SIP proxy. The CUBE pairs with your ITSP and routes calls to and from your Call Manager via SIP or H.323 (You could in theory use MGCP as well but I’m not covering it here).  Below is the topology that I am working with. Yours may look a little different and we’ll get into these differences as we progress.



ITSP Logical ConnectivityI mentioned topology differences and the biggest one is probably the firewall (ASA 5505) sitting between my CUBE and my ITSP. In an ideal world I’d give my CUBE router a public address and let it talk directly to the internet, this is not an ideal world. My ISP is small and stingy with their public IP addresses. It took a few fights and some extra cash to get one dedicated public IP on my ASA and getting a second is simply not worth the trouble. I’ve read all of the stories regarding trying to pass SIP through a firewall and while there are some caveats, I’ve made it work.

Connectivity is Everything…

It seems like a simple enough statement, but in terms of building and maintaining voice network connectivity really is everything. I prefer to keep it simple and the simplest way to build my topology was to keep the same protocol throughout. With the exception of the SCCP Phone (Call Manager does just fine translating SCCP to SIP and vice versa) every other connection is SIP.

  • Call Manager to CUBE & CUBE to Call Manager – SIP

By keeping the majority of my transactions SIP, I take away at least one point of failure. I mentioned earlier that you could configure the CUBE router connection to CM via H.323 (or even MGCP but that seems counter productive) and while I know that configuration can work just fine, why make it more complicated than it needs to be? The biggest thing to keep in mind when deciding on connectivity is “Can I troubleshoot it easily when it does not work?” Its a lot easier to look at a straight SIP trace.

Bring on the configs…

We’ll start with the CUBE first (This CUBE is running archaic 12.4 code).

The voice service commands are pretty standard. In the allow-connections section sip to sip is the key portion. Remember to configure your sip registrar settings here as well.


The next piece we’ll look at, are the voice translation rules. The first rule points my DID (I only have one in this scenario) to an extension on my CM. The second rule puts my DID as the number mask for all outgoing calls. Without this second translation, I’d have to do additional configurations in CM, the translation rule is easier.


Now, we’ll look at the dial-peers. I’ve got one for the incoming calls (from the ITSP) (Dial-peer 2) One for outgoing calls (I’m just dealing with LD calls right now) (Dial-peer 10) and one for communication with CM (Dial-Peer 100). Note where I applied my translation rules.


Finally, we’ll look at the SIP-UA (SIP User Agent) configuration. This is the actual heart & soul of CUBE. This is the connection and authentication to the ITSP. You may find that your ITSP we’ll peer with your specific public IP address rather than give you a user-id and/or password. Peering with an IP is in theory much more secure as spoofing an IP end to end is much more difficult. Notice the credentials and authentication sections. They both include a username and password. The credentials line identifies your CUBE to the ITSP and the authentication line gets you through door.


Next, we’ll take a look at the CM trunk configuration (My CM is 9.x)

First the initial configuration of the trunk. You’ll assign your device pool, media resources and things of that nature here…


Now, we’ll look at the incoming calls section of the trunk config. You’ll want to make sure that you direct inbound calls to the Calling Search Space that includes the Directory Numbers that you intend to answer the calls. You can also adjust things like significant digits. Generally speaking, I always want the CUBE/router to send me everything and then I’ll configure CM to pick and choose what it wants.


Finally, we’ll look at the connectivity section of the SIP trunk config. Here you’ll specify the address of your CUBE and your SIP and SIP Security profiles. These are standard profiles from Cisco and no tweaking is required to make this work.


Like most other things that Cisco creates, there are far more options in the trunk configuration than most configurations will require.

Finally, lets take a look at the ASA (This ASA is running 8.4(7) code)

First, we’ll take a look at my network and service objects. For this scenario, I defined the RTP range and SIP protocols. While not necessary, I defined SIP with both UDP and TCP entries.


Next, we’ll take a look at the NAT statements. While the CUBE is not a NAT aware SIP Proxy, the ASA provides some assistance in maintaining the end to end SIP headers required for successful peering and usage.


Finally, we’ll take a look at the access-list portion of the configuration. These are pretty straight forward…


Additional Notes…

The phone & route pattern configurations for this example are not impressive. The phone (7961) is configured with a Directory Number and pointed at a CSS with access to PSTN calling features. The basic route pattern is configured as 9.1XXXXXXXXXX and pointed at the SIP trunk created above. I discard the 9 (pre-dot) and send 11 digits to my ITSP. You don’t need the 9 but it keeps the scenario in line with most business systems.

I’ve struggled to find an ITSP that supports a true integration with the CUBE. There are several ITSPs that work with Asterisk and other open-source IP PBX platforms but CUBE is its own animal and as such these “Asterisk ITSPs” usually don’t work properly or in many cases don’t work at all. When I came across FlowRoute I was initially skeptical but as I’ve used their service more and more, I’ve become a bigger and bigger fan. The first thing that you’ll notice about FlowRoute is that anyone can try it out. Simply sign up and you’ll get some free time to peer with them and try your system out. If your system doesn’t work and if you aren’t happy with the performance, go another direction. If (and this is much more likely) you really enjoy the service. Deposit some money, purchase a DID and keep on going.

Final Thoughts…

I hope this example configuration has helped someone. What I’ve shown is not difficult and is actually quite simple when compared to other voice configurations. That being said, we all need to learn somewhere and hopefully I’ve helped someone do that.

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