Strange natd behavior.. just ignoring traffic?

Allen bsdlists at
Sat Nov 19 19:54:31 GMT 2005

I'm having a very odd situation here and no matter how I try, I can't wrap
my head around why it would even occur, much less how to fix it.

Imagine if you will:

fxp1 =,,,

fxp1 =

On NATBOX, the following ipfw rules:
00100 allow ip from any to any via lo0
00200 deny ip from any to
00300 deny ip from to any
10101 divert 10001 udp from 9300 to any in via fxp1
10102 divert 10001 udp from 2727 to any in via fxp1
10103 divert 10001 udp from 8000-8100 to any in via fxp1
65535 allow ip from any to any


Now I know that isn't the complete picture, but it's enough to illustrate
the behavior as long as natd is listening on 10001 which it is.

Rules 10101 and 10102 work as intended, traffic coming in is diverted to
natd for processing.

Rule 10103 NEVER hits, the counts are always zero, despite "tcpdump -ni
fxp1 host" showing tons of UDP traffic within the 8000-8100
port range.

Identical behavior is observed when using ipnat instead of natd, and I've
asked on the ipfilter list as well.

What in the world could cause this?  I've never seen anything like it.

Please CC directly, not subscribed to the list.

More information about the freebsd-questions mailing list