telnet: connect to address IPV6 Connection refused

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zahn-martin
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Re: telnet: connect to address IPV6 Connection refused

Post by zahn-martin » 2021/04/02 16:44:38

For my understanding it is a IPv6 issue.

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TrevorH
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Re: telnet: connect to address IPV6 Connection refused

Post by TrevorH » 2021/04/02 17:28:37

I suspect you have an external firewall in front of your machine that's blocking the connections.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

zahn-martin
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Re: telnet: connect to address IPV6 Connection refused

Post by zahn-martin » 2021/04/02 18:08:49

No - no external firewall.

zahn-martin
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Re: telnet: connect to address IPV6 Connection refused

Post by zahn-martin » 2021/04/03 07:05:19

Please note that the following services are open:

root@kamet:~> nmap -6 makalu.akadia.com

Starting Nmap 6.40 ( http://nmap.org ) at 2021-04-03 09:00 MEST
Nmap scan report for makalu.akadia.com (2a02:121e:58e2::1)
Host is up (0.0066s latency).
Not shown: 996 closed ports
PORT STATE SERVICE
22/tcp open ssh
53/tcp open domain
80/tcp open http
443/tcp open https
MAC Address: 8C:59:C3:D1:39:8A (Unknown)

Nmap done: 1 IP address (1 host up) scanned in 2.91 seconds

But not smtp - why not, I do not understand

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TrevorH
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Re: telnet: connect to address IPV6 Connection refused

Post by TrevorH » 2021/04/03 10:16:06

There is zero point in running nmap against the server from the server. As I already said, when you do that, the packets appear to come from localhost and are allowed.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

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jlehtone
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Re: telnet: connect to address IPV6 Connection refused

Post by jlehtone » 2021/04/03 12:33:26

Set tcpdump to listen smtp-port on makalu. Then attempt connect from kamet to makalu.

The obvious results are:
  • Nothing comes to makalu. Problem is not in makalu
  • Makalu replies with reject
  • Makalu replies ok, but not with IPv6/correct route
  • Successful connection

zahn-martin
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Re: telnet: connect to address IPV6 Connection refused

Post by zahn-martin » 2021/04/03 17:08:14

Sorry, I do not know what to to with tcpdump.

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TrevorH
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Re: telnet: connect to address IPV6 Connection refused

Post by TrevorH » 2021/04/03 17:28:32

yum install tcpdump
tcpdump port 25 -i $interface -n -nn -l

Amend $interface to reflect your external interface name. Ctrl-C to exit.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

zahn-martin
Posts: 35
Joined: 2020/05/05 19:44:15

Re: telnet: connect to address IPV6 Connection refused

Post by zahn-martin » 2021/04/03 18:24:10

Thank you all !

I tried tcpdump on makalu.akadia.com

tcpdump -i enp0s31f6 -vv dst makalu.akadia.com -n -nn -l (Port cannot be specified)

Then I try to connect from kamet:

telnet makalu.akadia.com 25

No output from tcpdump.

Regards Martin Zahn from Switzerland

zahn-martin
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Re: telnet: connect to address IPV6 Connection refused

Post by zahn-martin » 2021/04/03 18:31:51

Here the fully specified tcptump

root@makalu:~> tcpdump -i enp0s31f6 -vv dst makalu.akadia.com -n -nn -l and port 25
tcpdump: listening on enp0s31f6, link-type EN10MB (Ethernet), capture size 262144 bytes
CTRL-C

Again no connection from kamet.

What does that mean ?

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