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Date:      Thu, 21 Nov 2002 20:03:18 +0100
From:      Martin Stiemerling <Martin.Stiemerling@ccrle.nec.de>
To:        Scot Loach <sloach@SANDVINE.com>
Cc:        "'freebsd-net@freebsd.org'" <freebsd-net@FreeBSD.ORG>
Subject:   Re: Using ipfw to forward udp
Message-ID:  <3DDD2DF6.90005@ccrle.nec.de>
References:  <FE045D4D9F7AED4CBFF1B3B813C85337E5F45A@mail.sandvine.com>

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man ipfw says to fwd:
  fwd | forward ipaddr[,port]
Change the next-hop on matching packets to ipaddr, which can be
an IP address in dotted quad or a host name.  The search termi-
nates if this rule matches.
If ipaddr is a local address, then matching packets will be for-
warded to port (or the port number in the packet if one is not
specified in the rule) on the local machine.
If ipaddr is not a local address, then the port number (if speci-
fied) is ignored, and the packet will be forwarded to the remote
[...]

This is exactly the behaviour you're describing. May be the divert is 
more appropriate for your needs.

Martin


Scot Loach wrote:
> I'm trying to implement a type of transparent proxy for UDP.  My idea was to
> use ipfw to redirect all incoming UDP packets to my server, for example:
> 
> ipfw add fwd 127.0.0.1,9000 udp from any to any recv em0
> 
> However this doesn't seem to work: my server only receives UDP packets that
> are addressed to port 9000.
> 
> Can anyone suggest what I might be doing wrong?
> 
> thanks
> 
> scot.
> 
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-- 
Martin Stiemerling

NEC Europe Ltd. -- Network Laboratories  Stiemerling@ccrle.nec.de
IPv4: http://www.ccrle.nec.de  IPv6: http://www.ipv6.ccrle.nec.de


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