Re: outgoing tcp port 25 blocked? how to prove it?

Marco Moock <mm+usenet-es@dorfdsl.de> writes:

On 18.10.2024 um 11:03 Uhr Lesley Esen wrote:
>

Subject: outgoing tcp port 25 blocked? how to prove it?

>
Use traceroute -T -p 25 <target>
Check where the last reply comes from.
>
You can test with srv1.dorfdsl.de, this should reply in all cases.

FreeBSD's traceroute doesn't have the -T option.  So I don't know
informative this will be.  (I'm just learning about the -T and -p
options.  It seems very interesting and I don't know yet how it works.)

I cannot reach srv1.dorfdsl.de.

--8<-------------------------------------------------------->8---
%telnet srv1.dorfdsl.de 25
Trying 82.139.196.13...
telnet: connect to address 82.139.196.13: Operation timed out
Trying 2a01:170:118f:3::22...
telnet: connect to address 2a01:170:118f:3::22: No route to host
telnet: Unable to connect to remote host
%
--8<-------------------------------------------------------->8---

BTW, I don't know why modern telnet always tries an IPv6 in such cases.

(*) The traceroute to srv1.dorfdsl.de

--8<-------------------------------------------------------->8---
%traceroute -p 25 srv1.dorfdsl.de
traceroute to srv1.dorfdsl.de (82.139.196.13), 64 hops max, 40 byte packets
 1  * * *
 2  240.0.228.67 (240.0.228.67)  0.272 ms
    240.0.228.64 (240.0.228.64)  0.254 ms
    240.0.228.65 (240.0.228.65)  0.246 ms
 3  242.2.120.71 (242.2.120.71)  0.856 ms  1.913 ms
    242.2.120.195 (242.2.120.195)  1.009 ms
 4  240.3.180.10 (240.3.180.10)  0.880 ms
    240.3.180.11 (240.3.180.11)  0.935 ms
    240.3.180.9 (240.3.180.9)  1.526 ms
 5  242.10.82.177 (242.10.82.177)  1.471 ms
    242.10.90.183 (242.10.90.183)  2.239 ms
    242.2.213.197 (242.2.213.197)  1.199 ms
 6  38.32.206.149 (38.32.206.149)  0.604 ms
    100.100.4.78 (100.100.4.78)  1.399 ms
    204.68.252.113 (204.68.252.113)  1.151 ms
 7  * * *
 8  be3083.ccr41.dca01.atlas.cogentco.com (154.54.30.53)  56.042 ms
    be3084.ccr42.dca01.atlas.cogentco.com (154.54.30.65)  2.441 ms
    port-channel5392.ccr92.dca04.atlas.cogentco.com (154.54.40.49)  1.736 ms
 9  port-channel5042.ccr92.dca04.atlas.cogentco.com (154.54.162.221)  360.473 ms
    port-channel5927.ccr92.dca04.atlas.cogentco.com (154.54.163.101)  1.882 ms
    port-channel5042.ccr92.dca04.atlas.cogentco.com (154.54.162.221)  371.716 ms
10  be4188.ccr42.jfk02.atlas.cogentco.com (154.54.30.122)  58.424 ms
    be2317.ccr41.lon13.atlas.cogentco.com (154.54.30.186)  72.891 ms
    be2490.ccr42.lon13.atlas.cogentco.com (154.54.42.86)  72.750 ms
11  be2490.ccr42.lon13.atlas.cogentco.com (154.54.42.86)  72.794 ms  74.469 ms
    be12194.ccr41.ams03.atlas.cogentco.com (154.54.56.94)  86.506 ms
12  be12488.ccr42.ams03.atlas.cogentco.com (130.117.51.42)  131.634 ms
    be3874.rcr21.dus01.atlas.cogentco.com (154.54.62.229)  89.546 ms
    be12488.ccr42.ams03.atlas.cogentco.com (130.117.51.42)  88.654 ms
13  be3488.ccr42.lon13.atlas.cogentco.com (154.54.60.13)  92.094 ms
    be3875.rcr21.dus01.atlas.cogentco.com (154.54.73.25)  90.017 ms
    be3488.ccr42.lon13.atlas.cogentco.com (154.54.60.13)  92.073 ms
14  r0-36.00.3bw.tal.de (78.41.51.246)  90.619 ms  90.477 ms  90.669 ms
15  r4-68.bw.tal.de (78.41.51.91)  89.592 ms
    be3875.rcr21.dus01.atlas.cogentco.com (154.54.73.25)  91.501 ms
    r4-68.bw.tal.de (78.41.51.91)  87.113 ms
16  r1-3.bf.tal.de (78.41.51.133)  87.305 ms
    r4-68.bw.tal.de (78.41.51.91)  92.873 ms
    r1-3.bf.tal.de (78.41.51.133)  87.977 ms
17  srv1.dorfdsl.de (82.139.196.13)  112.620 ms *  97.974 ms
%
--8<-------------------------------------------------------->8---

(*) Now from a host that is not blocked at all

A telnet session first.

--8<-------------------------------------------------------->8---
%telnet srv1.dorfdsl.de 25
Trying 2a01:170:118f:3::22...
Connected to srv1.dorfdsl.de.
Escape character is '^]'.
220 srv1.dorfdsl.de ESMTP Sendmail 8.17.1.9/8.17.1.9/Debian-2+deb12u2; Fri, 18 Oct 2024 19:37:36 +0200; (No UCE/UBE) logging access from: kontesti.me(OK)-kontesti.me [IPv6:2600:3c03:0:0:f03c:91ff:fe96:40c1]
quit
221 2.0.0 srv1.dorfdsl.de closing connection
Connection closed by foreign host.
%
--8<-------------------------------------------------------->8---

Now the traceroute.  Looking at the traceroute, I can't tell the
difference between this host and the blocked-FreeBSD one.  Can you
clarify that a little?  Thanks!

--8<-------------------------------------------------------->8---
%sudo traceroute -T -p 25 srv1.dorfdsl.de
[sudo] password for dbastos:
traceroute to srv1.dorfdsl.de (82.139.196.13), 30 hops max, 60 byte packets
 1  10.206.9.32 (10.206.9.32)  0.072 ms  0.075 ms  0.068 ms
 2  10.206.35.101 (10.206.35.101)  0.211 ms  0.214 ms 10.206.35.102 (10.206.35.102)  0.226 ms
 3  10.206.32.1 (10.206.32.1)  3.712 ms  3.718 ms  3.714 ms
 4  lo0-0.gw1.cjj1.us.linode.com (173.255.239.101)  0.499 ms  0.377 ms  0.334 ms
 5  ae37.r02.lga01.ien.netarch.akamai.com (23.203.156.50)  1.580 ms ae31.r01.lga01.ien.netarch.akamai.com (23.203.156.16)  1.612 ms ae30.r02.ewr01.ien.netarch.akamai.com (23.203.154.42)  0.922 ms
 6  * nyk-b17-link.ip.twelve99.net (62.115.171.40)  2.001 ms  2.282 ms
 7  * * *
 8  ldn-bb2-link.ip.twelve99.net (62.115.139.247)  71.638 ms  71.720 ms *
 9  ldn-b3-link.ip.twelve99.net (62.115.122.181)  72.927 ms ldn-b3-link.ip.twelve99.net (62.115.120.75)  70.386 ms  70.375 ms
10  interlinkgmbh-ic-381329.ip.twelve99-cust.net (62.115.154.161)  69.886 ms  71.229 ms  70.610 ms
11  * * *
12  * * *
13  * * *
14  * * *
15  * * *
16  r4-fra1-de.as5405.net (94.103.180.7)  86.291 ms  86.283 ms  87.435 ms
17  cust-syseleven.fra1-de.as5405.net (45.153.82.5)  111.473 ms  111.469 ms  111.466 ms
18  r2-2.3bf.tal.de (78.41.51.242)  92.897 ms  92.305 ms  92.885 ms
19  * * *
20  srv1.dorfdsl.de (82.139.196.13)  114.786 ms  114.442 ms r4-fra1-de.as5405.net (94.103.180.7)  101.827 ms
--8<-------------------------------------------------------->8---