Date: Thu, 10 Jul 1997 12:27:22 -0400 (EDT) From: Charles Owens <owensc@enc.edu> To: hackers list FreeBSD <freebsd-hackers@freebsd.org> Cc: ari.suutari@ps.carel.fi Subject: ipfw rules processing order when DIVERTing Message-ID: <Pine.FBS.3.93.970710121015.10980C-100000@dingo.its.enc.edu>
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Hi all,
I'm a bit unsure about the order in which ipfw rules get processed in
relation to a DIVERT rule that calls natd(8). Note the last few sentences
from this excerpt from the natd(8) man page:
/sbin/ipfw -f flush
/sbin/ipfw add divert 6668 all from any to any via ed0
/sbin/ipfw add pass all from any to any
The second line depends on your interface and assumes that you've
updated /etc/services as above. If you specify real firewall rules,
---> it's best to specify line 2 at the start of the script so that natd
---> sees all packets before they are dropped by the firewall. The fire-
---> wall rules will be run again on each packet after translation by
---> natd, minus any divert rules.
If I take this as literally as I can, I interpret it as follows
* Rules before divert rule processed
* Divert rule ships all packets not dropped by above rules
to natd for address translation
* Packets return from natd and are then subjected to ALL rules,
except this time divert rule is skipped
This is somewhat counter-intuitive to me. If this how it works, what is
the reason for this design, since, as I think about it, there must be a
performance penalty to this approach (multiple passes of rules). I had
expected it to work like this:
* Rules before divert rule processed
* Divert rule ships all packets not dropped by above rules
to natd for address translation
* Packets return from natd and remaining rules after divert rule
are processed
What is the real story?
Thanks very much,
---
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Charles N. Owens Email: owensc@enc.edu
http://www.enc.edu/~owensc
Network & Systems Administrator
Information Technology Services "Outside of a dog, a book is a man's
Eastern Nazarene College best friend. Inside of a dog it's
too dark to read." - Groucho Marx
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