Windows Server 2003 IPSec Tunnel Connected, But Not Working (Possibly NAT/RRAS Related)
- by Kevinoid
Configuration
I have setup a "raw" IPSec tunnel between a Windows Server 2003 (SBS) machine and a Netgear FVG318 according to the instructions in Microsoft KB816514. The configuration is as follows (using the same conventions as the article):
NetA | SBS2003 | FVG318 | NetB
10.0.0.0/24 | 216.x.x.x | 69.y.y.y | 10.0.254.0/24
Both the Main Mode and Quick Mode Security Associations are successfully completed and appear in the IP Security Monitor. I am also able to ping the SBS2003 server on its private address from any computer on NetB.
The Problem
Any traffic sent from a computer on NetA to NetB, or from SBS2003 to NetB (excluding ICMP Ping responses), is sent out on the public network interface outside the IPSec tunnel (no encryption or header authentication, as if the tunnel were not there).
Pings sent from a computer on NetB to a computer on NetA successfully reach computers on NetA, but the responses are silently discarded by SBS2003 (they do not go out in the clear and do not generate any encrypted traffic).
Possible Solutions
Incorrect Configuration
I could have mistyped something, somewhere, or KB816514 could be incorrect in some way. I have tried very hard to eliminate the first option. Have re-created the configuration several times, tried tweaking and adjusting all the settings I could without success (most prevent the SA from being established).
NAT/RRAS
I have seen multiple posts elsewhere suggesting that this could be due to interaction between NAT and the IPSec filters. Possibly the NetA private addresses get rewritten to 216.x.x.x before being compared with the Quick Mode IPSec filters and don't get tunneled because of the mismatch. In fact, The Cable Guy article from June 2005 "TCP/IP Packet Processing Paths" suggests that this is the case, (see step 2 and 4 of the Transit Traffic path). If this is the case, is there a way to exclude NetA-NetB traffic from NAT?
Any thoughts, ideas, suggestions, and/or comments are appreciated.
