#1 terminates with an error "Connection refused".

[Anonymous]

The programm terminates with an error "Connection refused".
This seems to happen after the TCP response tothe TCP
connection attempt to the my own (external) IP address
(loopback test).
In this TCP response the ACK and the RST (reset) bit
are both set. I guess the reset bit is causing the
error "Connection refused".

My setup:

Internet
|
----------------------------
| 1st NAT (Zyxel 653 ? ME) |
----------------------------
|
----------------------------------
| 2nd NAT (Trendnet TEW 231 BRP) |
----------------------------------
|
-------------------------
| Host running natcheck |
-------------------------

(I know it is special due to the cascaded NATs...)

Software

Binary version natcheck-linux from webpage (on Aug,
20th 2005)

Output from natcheck:

myhost:~> ./natcheck-linux -v
server 1: pdos.lcs.mit.edu at 18.26.4.9:9856
server 2: tears.lcs.mit.edu at 18.26.4.77:9856
server 3: sure.lcs.mit.edu at 18.26.4.29:9856
Local TCP port: 44169
Local UDP port: 34230
Request 1 of 20...
Connection to server 1 complete
Connection to server 2 complete
Server 1 reports my UDP address as 83.180.76.234:28803
Server 2 reports my UDP address as 83.180.76.234:28803
Server 3 reports my UDP address as 83.180.76.234:28803
Server 1 reports my TCP address as 83.180.76.234:28801
Server 2 reports my TCP address as 83.180.76.234:28802
Initiated TCP server 3 connection
Initiated TCP loopback connection
checktcp connect: Connection refused

TCPdump:

22:07:08.569035 IP 192.168.2.22.34228 >
192.168.2.1.domain: 8370+ A? pdos.lcs.mit.edu. (34)
22:07:08.569920 IP 192.168.2.22.34229 >
192.168.2.1.domain: 9960+ PTR?
1.2.168.192.in-addr.arpa. (42)
22:07:08.618359 IP 192.168.2.1.domain >
192.168.2.22.34228: 8370 2/0/0 CNAME[|domain]
22:07:08.619123 IP 192.168.2.22.34230 >
192.168.2.1.domain: 8371+ A? tears.lcs.mit.edu. (35)
22:07:08.670226 IP 192.168.2.1.domain >
192.168.2.22.34230: 8371 1/0/0 A tears.lcs.mit.edu (51)
22:07:08.670472 IP 192.168.2.22.34230 >
192.168.2.1.domain: 8372+ A? sure.lcs.mit.edu. (34)
22:07:08.723698 IP 192.168.2.1.domain >
192.168.2.22.34230: 8372 2/0/0 CNAME[|domain]
22:07:08.724059 IP 192.168.2.22.44169 >
amsterdam.lcs.mit.edu.9856: S 1798729065:1798729065(0)
win 5840 <mss 1460,sackOK,timestamp 791629868
0,nop,wscale 2>
22:07:08.724094 IP 192.168.2.22.44169 >
tears.lcs.mit.edu.9856: S 1795141846:1795141846(0) win
5840 <mss 1460,sackOK,timestamp 791629868 0,nop,wscale 2>
22:07:08.724136 IP 192.168.2.22.34230 >
amsterdam.lcs.mit.edu.9856: UDP, length: 4
22:07:08.724146 IP 192.168.2.22.34230 >
tears.lcs.mit.edu.9856: UDP, length: 4
22:07:08.866612 IP amsterdam.lcs.mit.edu.9856 >
192.168.2.22.44169: S 2262936503:2262936503(0) ack
1798729066 win 57344 <mss 1400,nop,wscale
0,nop,nop,timestamp 2611963093 791629868>
22:07:08.866653 IP 192.168.2.22.44169 >
amsterdam.lcs.mit.edu.9856: . ack 1 win 1460
<nop,nop,timestamp 791630011 2611963093>
22:07:08.866738 IP 192.168.2.22.44169 >
amsterdam.lcs.mit.edu.9856: P 1:5(4) ack 1 win 1460
<nop,nop,timestamp 791630011 2611963093>
22:07:08.876250 IP tears.lcs.mit.edu.9856 >
192.168.2.22.44169: S 81336586:81336586(0) ack
1795141847 win 57344 <mss 1400,nop,wscale
0,nop,nop,timestamp 1012222372 791629868>
22:07:08.876275 IP 192.168.2.22.44169 >
tears.lcs.mit.edu.9856: . ack 1 win 1460
<nop,nop,timestamp 791630020 1012222372>
22:07:08.876333 IP 192.168.2.22.44169 >
tears.lcs.mit.edu.9856: P 1:5(4) ack 1 win 1460
<nop,nop,timestamp 791630020 1012222372>
22:07:08.882061 IP amsterdam.lcs.mit.edu.9856 >
192.168.2.22.34230: UDP, length: 12
22:07:08.888816 IP tears.lcs.mit.edu.9856 >
192.168.2.22.34230: UDP, length: 12
22:07:08.889701 IP
supervised-residence.lcs.mit.edu.9856 >
192.168.2.22.34230: UDP, length: 12
22:07:09.011929 IP amsterdam.lcs.mit.edu.9856 >
192.168.2.22.44169: P 1:13(12) ack 5 win 58296
<nop,nop,timestamp 2611963238 791630011>
22:07:09.011961 IP 192.168.2.22.44169 >
amsterdam.lcs.mit.edu.9856: . ack 13 win 1460
<nop,nop,timestamp 791630156 2611963238>
22:07:09.013353 IP amsterdam.lcs.mit.edu.9856 >
192.168.2.22.44169: F 13:13(0) ack 5 win 58296
<nop,nop,timestamp 2611963238 791630011>
22:07:09.052506 IP 192.168.2.22.44169 >
amsterdam.lcs.mit.edu.9856: . ack 14 win 1460
<nop,nop,timestamp 791630197 2611963238>
22:07:09.135651 IP tears.lcs.mit.edu.9856 >
192.168.2.22.44169: . ack 5 win 58296
<nop,nop,timestamp 1012222632 791630020>
22:07:09.170825 IP tears.lcs.mit.edu.9856 >
192.168.2.22.44169: P 1:13(12) ack 5 win 58296
<nop,nop,timestamp 1012222667 791630020>
22:07:09.170852 IP 192.168.2.22.44169 >
tears.lcs.mit.edu.9856: . ack 13 win 1460
<nop,nop,timestamp 791630315 1012222667>
22:07:09.171003 IP 192.168.2.22.44169 >
supervised-residence.lcs.mit.edu.9856: S
1803502092:1803502092(0) win 5840 <mss
1460,sackOK,timestamp 791630315 0,nop,wscale 2>
22:07:09.171040 IP 192.168.2.22.44170 >
d83-180-76-234.cust.tele2.ch.28802: S
1800938743:1800938743(0) win 5840 <mss
1460,sackOK,timestamp 791630315 0,nop,wscale 2>
22:07:09.172897 IP tears.lcs.mit.edu.9856 >
192.168.2.22.44169: F 13:13(0) ack 5 win 58296
<nop,nop,timestamp 1012222667 791630020>
22:07:09.177549 IP d83-180-76-234.cust.tele2.ch.28802 >
192.168.2.22.44170: R 0:0(0) ack 1800938744 win 0
22:07:09.212490 IP 192.168.2.22.44169 >
tears.lcs.mit.edu.9856: . ack 14 win 1460
<nop,nop,timestamp 791630357 1012222667>
22:07:09.319214 IP
supervised-residence.lcs.mit.edu.9856 >
192.168.2.22.44169: R 0:0(0) ack 1803502093 win 0
22:07:09.319553 IP 192.168.2.22.44169 >
amsterdam.lcs.mit.edu.9856: F 5:5(0) ack 14 win 1460
<nop,nop,timestamp 791630464 2611963238>
22:07:09.319575 IP 192.168.2.22.44169 >
tears.lcs.mit.edu.9856: F 5:5(0) ack 14 win 1460
<nop,nop,timestamp 791630464 1012222667>
22:07:09.458961 IP amsterdam.lcs.mit.edu.9856 >
192.168.2.22.44169: . ack 6 win 58296
<nop,nop,timestamp 2611963685 791630464>
22:07:09.465020 IP tears.lcs.mit.edu.9856 >
192.168.2.22.44169: . ack 6 win 58296
<nop,nop,timestamp 1012222962 791630464>

cheers,
Bernie (bhoeneis@hoeneisen.ch)