Date: Sat, 18 Apr 2015 20:57:58 +0200 From: Daniel Haid <d.haid@gogi.tv> To: freebsd-pf@freebsd.org Subject: NAT fails to correctly translate udp port numbers embedded in certain ICMP error packets Message-ID: <20150418205758.6710b3bc@paperino>
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Hi, I think I found a bug in the NAT of the packet filter, but I am not sure. My setup is as follows. client (linux) | | bridge0, mtu=1500 | pfsense 2.2.2 (FreeBSD 10.1-RELEASE-p9) | | pppoe0, mtu=1492 | internet On the client, I run the following command: # nping --udp 8.8.8.8 -g 10000 -p 20000 --data-length 1472 --df This generates five UDP packets of IP length 1500, set the do not fragment option, and send them from source port 10000 to destination port 20000. I have verified by packet capture that this really happens. As the mtu of the pppoe link is 1492, the packets cannot reach their destination, so pfsense generates "ICMP fragmentation needed" error packets. I expect five such packets, and I indeed receive five, but the first one (!) seems to be corrupted, as I will now explain. I run the following command (with following output) on pfsense: # pfctl -s state | grep 10000 bridge0 udp 8.8.8.8:20000 <- 10.0.0.101:10000 NO_TRAFFIC:SINGLE pppoe0 udp 84.112.84.112:59518 (10.0.0.101:10000) -> 8.8.8.8:20000 SINGLE:NO_TRAFFIC Each of the five ICMP packets should have embedded the header of the respective offending 1500-byte packet. The NAT should appropriately map the port numbers. However, the first packet receieved from the client has source port 59518 (the untranslated one) in the UDP header embedded in the ICMP packet. The other four ICMP packets are fine (source port 10000, which is the correct, translated, value). Note that this only happens for ICMP error packets originating at the pfsense router itself. ICMP error packets of the same type but from a router in the public internet are always translated correctly (all five!) before being forwarded to the client. For reference, I have added the output of pfctl -s nat below. --DH no nat proto carp all nat-anchor "natearly/*" all nat-anchor "natrules/*" all nat on pppoe0 inet from 127.0.0.0/8 to any port = isakmp -> 84.112.84.112 static-port nat on pppoe0 inet from 10.0.0.0/24 to any port = isakmp -> 84.112.84.112 static-port nat on pppoe0 inet from 127.0.0.0/8 to any -> 84.112.84.112 port 1024:65535 nat on pppoe0 inet from 10.0.0.0/24 to any -> 84.112.84.112 port 1024:65535 no rdr proto carp all rdr-anchor "relayd/*" all rdr-anchor "tftp-proxy/*" all rdr-anchor "miniupnpd" all
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