[rbldnsd] filtering udp 53?

[joe]

Hello,

When I start up rbldnsd, it binds to udp port 53, yet nmap says that
port is filtered, and digging locally doesn't work:
---------------------------------
beta:/home/joe# rbldnsd -b localhost list:ip4set:list
rbldnsd: listening on 127.0.0.1/53
rbldnsd: ip4set:list: 20070202 054623: e32/24/16/8=1/0/0/0
rbldnsd: zones reloaded, time 0.0e/0.0u sec, mem arena=132 free=111 mmap=0 Kb
rbldnsd: rbldnsd version 0.994b (16 Apr 2005) started (1 socket(s), 1 zone(s))
beta:/home/joe# nmap -sU localhost -p 53

Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2007-02-01 21:47 PST
Interesting ports on beta.joew.net (127.0.0.1):
PORT   STATE         SERVICE
53/udp open|filtered domain

Nmap finished: 1 IP address (1 host up) scanned in 0.332 seconds
beta:/home/joe# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
beta:/home/joe# dig +short @localhost 192.168.0.123
beta:/home/joe#
---------------------------------

any ideas? I'm positive I don't have any firewalls running, and tested
this on freebsd/linux with the same results. Why is rbldnsd filtering
this?

Thanks,
Joe