FIX: Client computers cannot access an L2TP server or an IPSec endpoint through a Threat Management Gateway 2010 server array that uses network load balancing

Consider the following scenarios:

Scenario 1:

• You have servers that are running Microsoft Forefront Threat Management Gateway 2010 (TMG) Service Pack 1 (SP1) with Integrated Network Load Balancing (NLB).
• You have at least 2 network adapters, and you let Internet Protocol security (IPsec) and Layer 2 Tunneling Protocol (L2TP) traffic through the TMG array to a remote destination.
• A route relationship is configured in TMG between networks where IPsec and L2TP/IPsec will be forwarded. 
• Some internal client computers use IPsec or L2TP/IPsec to connect to a server on the other network. The other network can be an external or perimeter network.

Scenario 2:

• You have servers that are running TMG SP1 with NLB.
• You have at least 2 network adapters, and you enable IPsec or L2TP traffic through the TMG array to a remote destination.
• A network address translation (NAT)relationship is configured in TMG between networks where IPsec and L2TP/IPsec will be forwarded. 
• Some internal client computers use IPsec or L2TP/IPsec to connect to a server on the other network. The other network can be an external or perimeter network.

In these scenarios there is an NLB and TMG integration failure, and the client computers that use IPsec or L2TP/IPsec cannot connect to a server on the external or perimeter network.