Kerberos authentication on Windows Server 2003 through router/firewall

Given is the following network setup:

┌192.168.1.10    Windows Server (WAN)
│
└192.168.1.100   Router         (WAN)
  192.168.0.1    Router         (LAN)
  │
  └192.168.0.x   Windows Client (LAN)

WAN area: 192.168.1.x.

LAN area: 192.168.0.x.

Those areas are separated by the router.

As you can see the Client is located in the LAN area, and connected to the WAN area through a router. The Server is located at the WAN area. What I want to do is enable the Client (which is running Windows 7) to do authentication via Kerberos with the Server (Windows Server 2003).

Many websites telling me I need to enable TCP und UDP port 88 in the router firewall to use Kerberos. Of course, this only makes sense if the server is behind a firewall. But in this case the client(s) is (are) behind a firewall.

I tried to use the lmhosts-file on the client to specify the IP addresses of my Windows Server, but it doesn't work. I am able to do the windows logon on my client using the domain user and password. But when I want to access a network share, for example, I get an error message and I am prompted to do the authentication again.

My question: What configuration do I need to authenticate to the Windows Domain correctly and use the network share without having to re-authenticate?