An IPsec Virtual Private Network or VPN, is sometimes used as a backup route for a Wide Area Network failure. VPN’s are typically deployed as a “tunnel” through the Internet and as such are “point to point” solutions by definition. Unfortunately that will not get the job done for a VoIP deployment! If you have ever deployed ShoreTel over a VPN in a multi site network that has more than two sites, you will note that it has problems. The first problem you will note is that the Switch Connectivity display within the ShoreTel ShorewareDirector management portal looks like a Christmas tree. Normally in a finally tuned network you should see all green in the connectivity display. In an IPsec VPN network, using a “hub and spoke” implementation or “point to point” links you will see lots of Red and Yellow boxes and switch connectivity will be inconclusive at best.
Next, you will undoubtedly experience instances of “one way audio”. Again, this is because an IPsec VPN is a “point to point” solution, when you really require a fully messed solution that can handle more than unicast packet transfers. Additionally, as IPsec applies encryption based on a “shared key” so the two end points must possess the key! IPsec does not support Multicast or Broadcast and this make it less then desirable for a VoIP deployment. Unicast is when you address the source and destination IP address to a specific target device. Broadcast is used when you must sent to all network devices because you do not know the destination address. Multicast is used when you send to a group of devices that monitor a target IP address for network management and service subscriptions. Using an IPsec point to point VPN might get your phones to register and enable you to make phone calls, but you will be plagued by network connectivity issues that will make your VoIP deployment problematic. Your technical support center or help desk phones will be constantly ringing with unhappy users and incomplete phone calls.
You don’t have to be a Network guru to understand a “hub and spoke” topology. All communications between devices at different sites (i.e. spoke end points) must traverse the hub site if they are to communicate between each other. This might work for unicast communication, but it is inefficient and invites disaster. For two sites (i.e. spokes) to communicate the have to go through the hub, unpacking and repacking, encrypting and decrypting, sharing keys before resending packets to the ultimate destination. Assuming you are using this configuration only as a backup during a real WAN disaster, this might be acceptable temporarily. Using IPsec VPN “hub and spoke” topology in a ShoreTel VoIP deployment, it is not very useful. We have two issues: first, IPsec does not support anything other than Unicast communication; and secondly “hub and spoke” is unworkable because “spoke to spoke” communication is required.
How do we solve this? Fortunately there are two strategies that fit the bill perfectly. First, GRE or ‘generic routing encapsulation’ should be used to support broadcast and multicast communications, a core component of any network deployment, especially those of a VoIP variety. Secondly, DMVPN or “dynamic multipoint virtual private network’ technology should be implemented to assure “spoke to spoke” communications. DMVPN, which employs mGRE (muti-point GRE) and Dynamic Next Hop Router Resolution protocol (DNHRP) technologies make it possible to deploy a ShoreTel VoIP solution over the public internet and achieve MPLS like connectivity at a fraction of the cost. Given sufficient bandwidth, this should be more than adequate.
What about encryption you might ask? ShoreTel, CISCO and most VoIP solutions provide encryption at the network and transport level anyway, so this component may not be needed. If you are also moving data over this mesh, then you can use DMVPN in conjunction with IPsec to assure confidentiality, integrity and authentication (i.e. CIA). The issue is that a fully meshed communications network is absolutely obtainable with VPN technology, but you have to implement the correct protocol to achieve the desired results!
WAN configuration is an exact science as is ShoreTel and CISCO VoIP technology. If you are fortunate to have that level of expertise in one individual or one vendor, then you are moving in the right direction with your VoIP deployment. If you need help in the WAN aspect of VoIP, then you need to call on DrVoIP. We can make the network.