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TMG ISP Redudancy and DNS

Hello Experts,

actually this is the continuation of my previous question


I have installed TMG with 3 NICs such as ISP1, ISP2 and Internal

I configured the ISP1 and ISP2 interfaces with IP addresses and default gateways and

configured internal NIC with IP address, but no  Default Gateway.

I installed DNS service on TMG and configured the forwarders pointing to ISP DNS servers.

Finally Internal NIC DNS configuration as follows

Primary :

Alternative: Internal AD DNS servers

Configured persistent routes

Persistent Routes:
  Network Address          Netmask             Gateway Address  Metric                             1                  ( Internal LAN)
            2                   ( ISP1 DNS Server)
            3                    ( ISP2 DNS Server)

Suddenly I started facing a problem that web proxy client receiving a pop up Authentication Required.

I tried nslookup on TMG server for my domain domain but cannot resolved.

I would highly appreciate any help.

Avatar of Techrunner


I uninstall TMG and removed the server from the domain.

When I am trying to rejoin, it says the domain name cannot be resolved and the failed to join to domain

Still the interface and route configuration remain as mentioned above.

Avatar of Craig Beck
You don't particularly need DNS server to be installed on the TMG if you only want it to resolve hostnames for web clients.

The TMG server will use the DNS server addresses you configure on the internal NIC (or External NIC) to resolve URLs on the client's behalf.  The DNS server is only necessary if you want to forward internal URLs to your internal hosts/DNS servers.
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Craig Beck
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What is your recommedation for DNS ? Actually I dont keep any ISP's DNS server forwarder on my internal DNS server

Your internal DNS server should use your ISP DNS servers as forwarders to ensure you get a fast response.  You don't have to use forwarders though, but if you don't you must use the Root servers or you won't resolve any external URLs.
How about this if I configure a conditional forwarder on TMG server and to forward DNS request to  internal DNS Server which is responsible for AD.
If you need internal clients to get to internal web sites then that's fine as the TMG will be proxying, but if you don't need any internal clients to get to internally-hosted websites there's not much point in running DNS on the TMG unless you want to manipulate URLs (block access to sites using DNS, etc).
So far now everything is working.

Just a summary

- Installed the DNS service on TMG.
- Configured the forwarders pointing to ISP 1 & 2 DNS servers.
- Configured the conditional forwarder to forward DNS request to internal DNS server for AD authentication.
- Internai NIC DNS

Primary : ( local host TMG
Alternative: Internal DNS servers.
Thanks craigbeck Its working fine.

But just facing some slowness browser though I have only 1 user connected

ISP1 Leased Line 15MB


I posted a new question with a new design. Please can you help in this.

Thanks :)