ipfw questions: how to forward incoming TCP connections from the same host?

[Yuri]

I need to forward incoming TCP connections made to my host 192.168.5.3 
on the port 3100 to the IP address 10.0.0.101 port 3000 connected 
through another interface.


These rules work when connection is made from a remote host:

ipfw -q nat 19001 config redirect_port tcp 10.0.0.101:3000 192.168.5.3:3100

ipfw -q add 19001 nat 19001 tcp from any to 192.168.5.3 3100 in recv sk0

ipfw -q add 19001 nat 19001 tcp from 10.0.0.101 3000 to any out xmit sk0


Question#1: How to allow connections from the same host to be forwarded 
the same way?


Connections from the host's LAN IP address pass through lo0, but this 
rule doesn't work when added:

ipfw -q add 19001 nat 19001 tcp from 192.168.5.3 to 192.168.5.3 3100 in 
recv lo0

Wireshark shows that the incoming connection is from 192.168.5.3 to 
192.168.5.3 on 3100 but it gets immediately rejected instead of being 
forwarded.

This rule looks very similar to the second rule above, just the 
interface is different. Why doesn't it work?


Question#2: When lo0 is added to the third rule above it stops working 
for the return traffic:

ipfw -q add 19001 nat 19001 tcp from 10.0.0.101 3000 to any out xmit sk0 
xmit lo0

Just adding "xmit lo0" makes it to fail for sk0 too.

When several interfaces are present in the rule, doesn't this mean that 
it should apply to all of them?

Perhaps multiple interfaces can only be used in recv/xmit combination? 
Why does this command accept two xmit clauses then?


Thank you,

Yuri