[opensuse] nfs server /require/ reverse DNS lookup working?!

Dear list

I have learned long time ago that NFS require working reverse DNS
lookup. Below is quote from
http://www.yiluda.net/manual/linux/rute/node31.html

Sharing a directory with a remote machine requires that forward and
reverse DNS lookups be working for the server machine as well as all
client machines.

However, I have been using NFS a few years and never actually worried
about it: my office network and the whole campus network do not have
reverse dns setup and running, yet I am able to set up and use NFS just
fine. The client and server are both SuSE, also Gentoo, Ubuntu and
Debian are being used as NFS client, no problem! No reverse DNS lookup!
Until one day I try to add a Windows client and I got a problem.

After installed NFS client on Windows (this is part of Microsoft's
product "Services for Unix"), I try to access NFS share '/home/packman'
on the NFS server and was told access denied. Then check SuSE Linux NFS
server log and I see this:

Apr 9 14:58:29 joe mountd[17301]: can't get hostname of 218.193.55.201
Apr 9 14:58:29 joe mountd[17301]: can't get hostname of 218.193.55.201
Apr 9 14:58:29 joe mountd[17301]: refused mount request from 218.193.55.201 for /home (/): not exported
Apr 9 14:58:29 joe mountd[17301]: can't get hostname of 218.193.55.201
Apr 9 14:58:48 joe mountd[17301]: can't get hostname of 218.193.55.201
Apr 9 14:58:53 joe su: (to root) zhangweiwu on /dev/pts/2
Apr 9 14:58:58 joe mountd[17301]: can't get hostname of 218.193.55.201
Apr 9 15:18:35 joe syslog-ng[4024]: STATS: dropped 0
Apr 9 15:46:47 joe mountd[17301]: refused mount request from 218.193.55.201 for /home (/): not exported
Apr 9 15:46:57 joe mountd[17301]: can't get hostname of 218.193.55.201

This is the first time I see mount failed because reverse DNS lookup
failed. My dumb questions are:

1. If reverse lookup had been a must, why I hadn't have this problem
with Linux clients?
2. Can I turn off reverse lookup on the DNS server? It's impossible
for me to set up reverse lookup because client is not in the
network managed by me and I don't see how reverse lookup offered
better security: because I only export read-only shares!

Thanks in advance!

my /etc/exports (using SuSE 10.2), FYI:

joe:/home/zhangweiwu # cat /etc/exports
/home/packman/ *(ro,no_subtree_check,insecure,sync)


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