Fail to lookup virutal domain name.

[Sam Wun]

HI,

I have 3 domain names in my server, fastline.bidbid.com,
mishi.bidbid.com
and www.sam.com, where www.sam.com is a virtual host.
fastline.bidbid.com
is pointing at 192.168.1.1, mishi.bidbid.com is pointing at
172.16.1.1, and www.sam.com also pointing at 172.16.1.1,  thus:

fastline.bidbid.com -> 192.168.1.1
mishi.bidbid.com -> 172.16.1.1
www.sam.com -> 172.16.1.1

when I do nslookup on the www.sam.com ( the virtural name), it shows:

swun at fastline ~ > nslookup www.sam.com
Server:  fastline.bidbid.com
Address:  192.168.1.1

Name:    www.sam.com
Address:  172.16.1.1

But the following may not be right?

swun at fastline ~ > nslookup 172.16.1.1
Server:  fastline.bidbid.com
Address:  192.168.1.1

Name:    mishi.bidbid.com
Address:  172.16.1.1

I would expect nslookup 172.16.1.1 should show me the Name www.sam.com
as
well?
What may be wrong with my setting then?

Here is my db.sam zone file:
swun at fastline /etc/namedb > cat db.sam
$TTL 432000
@ IN  SOA sam.sam.com. root.sam.sam.com. ( 2000090700 10800 3600 604800
86400 )
  IN  NS  sam.sam.com.

localhost            IN  A     127.0.0.1
sam                  IN  A     172.16.1.1
sam                  IN  MX    10 sam.sam.com.

www.sam.com.         IN  A     172.16.1.1

And my db.172.16.1.1 file:
swun at fastline /etc/namedb > cat db.172.16.1
$TTL 432000
@ IN  SOA fastline.bidbid.com. root.fastline.bidbid.com. ( 2000090700
10800
3600 604800 86400 )
  IN  NS  fastline.bidbid.com.
  IN  NS  mishi.bidbid.com.

1.1.16.172.IN-ADDR.ARPA.        IN  PTR   mishi.bidbid.com.
200.1.16.172.IN-ADDR.ARPA.      IN  PTR   db.bidbid.com.

1.1.16.172.IN-ADDR.ARPA.        IN  PTR   www.sam.com.
1.1.16.172.IN-ADDR.ARPA.        IN  PTR   www.rolandx.com.
1.1.16.172.IN-ADDR.ARPA.        IN  PTR   www.fineworkx.com.

Thanks
Sam