Date: Tue, 30 Jun 2015 21:20:39 +0200 From: Georgios Amanakis <g_amanakis@yahoo.com> To: freebsd-ipfw@freebsd.org Subject: keep-state and in-kernel NAT exposes local ip on external interface Message-ID: <1435692039.18121.12.camel@yahoo.com>
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On FreeBSD 10.1p13 with two interfaces em0(internet) and em1(lan) I can fish (tcpdump)packets on em0 which have escaped the in-kernel NAT and have as source address an IP on the LAN. This should not happen and I can confirm that with pf this is not the case. I have the following ipfw rules: nat: ipfw nat 123 config ip xxx.xxx.xxx.xxx same_ports reset 00100 reass ip from any to any in 00200 allow ip from any to any via lo0 00300 allow ip from any to any via em1 00400 nat 123 ip from any to any in recv em0 00500 check-state 00600 skipto 24000 ip from any to me dst-port 80,443,22,500,4500,1194,993,8112 in recv em0 keep-state 00700 skipto 24000 ip from any to any out xmit em0 keep-state 00800 deny log ip from any to any 24000 nat 123 ip from any to any out xmit em0 24100 allow ip from any to any Contrary to many online tutorials, including the example of the handbook regarding NAT ( https://www.freebsd.org/doc/handbook/firewalls-ipfw.html), when one places the NAT rules with the opposite order (i.e. outbound rule first and then the inbound rule) the problem disappears. i.e. ... 00400 nat 123 ip from any to any out xmit em0 ... 24000 nat 123 ip from any to any in recv em0 ... Why is this happening? Any objections to reversing the order of the NAT rules?
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