TMG Traffic For a Specific IP isn't leaving the server despite valid routes and no firewall

Question

Hi,
 I'm struggling to troubleshoot a TMG networking issue:
I have a TMG server setup in my DMZ. Inbound traffic hits the a 3rd party firewall router, goes to the TMG server and is then routed back through the 3rd party firewall router to my internal network. I've setup web publishing rules and listeners for IIS
sites and SMTP traffic using a different IP to listen for 2 different websites and another IP for SMTP.
The issue I have is that my TMG server can't ping a server on the internal network on a specific IP:
TMG can ping 192.168.11.190
TMG cannot ping 192.168.11.191
Firewall rules are configured to permit traffic (no deny connections are shown in the monitor).
tracert and pings to 192.168.11.190 hit the internal IP of the 3rd party router
tracert to 192.168.11.191 simply responds with * * * * before timing out
Monitoring from within TMG shows the correct IP is being used in both cases (internal NIC 192.168.10.10).
A route print from TMG has a valid route to the internal network:
(network)192.168.11.128 (mask) 255.255.255.128 (gateway) 192.168.10.126
In summary:
 - TMG can ping 192.168.11.190, but not 192.168.11.191
 - Valid routes exists 
 - No firewall rules are blocking communication
 - Traffic to 192.168.11.191 doesn't seem to be leaving the TMG server 
Any advice on solving this would be appreciated.
Cheers

Answer 1

It can have many reasons, but it appears to me you are having a routing issue. I can't say for sure, because I don't have the entire IP Addressing sheme. I assume you have used separate subnets for the External DMZ and Internal DMZ.
Have you configured the 192.168.11.128/25 subnet as a correct 'Address' range 192.168.11.128 - 192.168.11.255 on the 'Internal' interface within TMG?
Boudewijn Plomp | BPMi Infrastructure & Security
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