xdmcp and dns

[Andrew Bell Test]

Hello list,

I'm running RHEL 3 with xdmcp enabled for remote X11 using gdm. We have
cygwin running on windows PC's connecting to the Linux machine. 

My problem is that cygwin was failing to connect to the Linux box when
the second Linux NIC (NIC1) was up. 

After trawling the logs I found the initial part of the handshaking for
a failed gdm connect went like this:

Dec 16 10:55:03 compileserver gdm[2916]: gdm_xdmcp_decode: Received
opcode QUERY from client 192.168.0.5
Dec 16 10:55:03 compileserver gdm[2916]: gdm_xdmcp_send_willing: Sending
WILLING to 192.168.0.5
Dec 16 10:55:04 compileserver gdm[2916]: gdm_xdmcp_decode: Received
opcode REQUEST from client 192.168.0.5
Dec 16 10:55:14 compileserver gdm[2916]: gdm_auth_secure_display:
Setting up access for 192.168.0.5:0 - 1 entries
...

Where as a successful connect with Nic1 lo went like this:

Dec 16 10:55:03 compileserver gdm[2916]: gdm_xdmcp_decode: Received
opcode QUERY from client 192.168.0.5
Dec 16 10:55:03 compileserver gdm[2916]: gdm_xdmcp_send_willing: Sending
WILLING to 192.168.0.5
Dec 16 10:55:04 compileserver gdm[2916]: gdm_xdmcp_decode: Received
opcode REQUEST from client 192.168.0.5
Dec 16 10:55:14 compileserver gdm[2916]: gdm_auth_secure_display:
Setting up access w2kantonyja.devnet.com:0 - 1 entries
...

Ahh I thought, so gdm_auth_secure_display is failing to resolve
192.168.0.5 to w2kantonyja.devnet.com. NIC1 was using DHCP and peerdns
was set to true. After inspecting the resolv.conf I found the nameserver
was being issued erroneously therefore no gethostbyname. Great. I have
no control over the router issuing the dns server via a client dhcp
request, so I've temporarily assigned Nic1 a static IP and turned off
peerdns, then manually adjusted /etc/resolv.conf to point at the
nameserver running locally. Now I can do a host 192.168.0.5 which
correctly returns w2kantonyja.devnet.com. I thought this would suffice,
but no, still can't use cygwin with Nic1 up. So in shear desperation
I've added the host names to /etc/hosts and it all works perfectly.

My question is what's wrong with my reverse dns lookup if host
xxx.xxx.xxx.xxx returns a hostname locally, why does gdm still fail to
correctly resolve IP -> Hostname for the gdm auth ?

TIA

Andrew. 
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