Re: FTP and connection tracking

["Haitao Yu" <yuht@th-dascom.com.cn>]

As I think, ftp nat's expected function is called twice when the first expected packet is in PREROUTING chain and POSTROUTING chain.

>Dear list
>
>I am currently developing an application which is using DNAT and 
>masquerading. First an incoming packet is DNAT'ed to have as specific dest. 
>ip. The it is masquerading when it is leaving the decided interface.
>
>This works fine, but when I use FTP, the following shows up in the kernel 
>log:
>
><4>ip_conntrack_in: related packet for c3a22310
><4>nat_expected: We have a connection!
><4>nat_expected: PASV cmd. 192.168.1.254->192.168.4.1
><4>nat_expected: IP to 192.168.4.1
><4>Found best for tuple c3d69db8: 6 10.0.0.8:1026 -> 192.168.4.1:11697
><4>nat_expected: We have a connection!
><4>nat_expected: PASV cmd. 192.168.1.254->192.168.4.1
><4>nat_expected: IP to 192.168.1.254
><4>Found best for tuple c3d69cf0: 6 192.168.1.254:1026 -> 192.168.4.1:11697
><4>Altering reply tuple of c3a22310 to tuple c3d69cd0: 6 192.168.4.1:11697 
>-> 192.168.1.254:1026
><4>Mangling c3ad4140: SRC to 192.168.1.254 1026
><4>Confirming conntrack c3a22310
>
>My question is:
>Why does: "We have a connection!" and the following lines show up two times? 
>Is the connection data traversing the same chain twice?
>
>Does anybody know where I can find more information on how the code in 
>connection tracking and NAT works?
>
>Thanks in advance.
>
>/Hans
>
>
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               Haitao Yu
               yuht@th-dascom.com.cn
					2002-12-17