Date: Sat, 26 Jul 2003 11:13:59 +0400 From: Yar Tikhiy <yar@comp.chem.msu.su> To: Clement Laforet <sheepkiller@cultdeadsheep.org> Cc: durham@jcdurham.com Subject: Re: NATD and Address Redirection Message-ID: <20030726071359.GA61353@comp.chem.msu.su> In-Reply-To: <20030726022205.452c374f.sheepkiller@cultdeadsheep.org> References: <200307251349.38413.durham@jcdurham.com> <20030726022205.452c374f.sheepkiller@cultdeadsheep.org>
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On Sat, Jul 26, 2003 at 02:22:05AM +0200, Clement Laforet wrote: > > for incoming traffic, you must use -redirect_address, but for outgoing > you have to set -alias_address. > If you want to use a specific public IP to map incoming AND outgoing > packets, you need to run 2 natd, using ipfw matching. I'm afraid this is not exactly correct. IIRC when 5 years ago I was hacking natd and libalias to use them for transparent HTTP proxying, their internals looked rather clear. In a nutshell, they were as follows. There was a translation table inside libalias with 3 columns in it: the internal connection point (IP&port), alias point, and external point. When a packet was heading outside, its source IP&port were matched against the "internal" column, and its destination IP&port against the "external" column. If an entry were found, the packet's source IP&port would be replaced with the values from the "alias" column. When a packet was going in the opposite direction, inside, its source IP&port were matched against the "external" column, and its destination IP&port against the "alias" column. Then the packet's destination IP&port were replaced with the values from the "internal" column of the entry found. By specifying a redirect_address rule, just an entry was inserted to that table with a wildcard value for all the ports and for the external IP address. Upon matching, such an entry would clone into a new one containing the information specific for a particular session. Thus the solution was symmetric by design, without requiring 2 natd's or additional ipfw rules. P.S. As I can see, today's libalias still uses the same approach. -- Yar
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