Tymur Gubayev's questions -server

Tymur Gubayev

Asked: 2022-02-25 01:11:25 +0800 CST

nmap reports ftp port open when the server is actually shut down

0

nmap output:

$ sudo nmap -PN 1.2.3.4
Starting Nmap 7.92 ( https://nmap.org ) at 2022-02-24 09:58 CET
Nmap scan report for 1.2.3.4
Host is up (0.035s latency).
Not shown: 999 filtered tcp ports (no-response)
PORT   STATE SERVICE
21/tcp open  ftp

Nmap done: 1 IP address (1 host up) scanned in 8.80 seconds

This happened twice now, with a server that was literally not running because it hat no power, and now another one - which actual state I don't know exactly, there is most probably some firewall between. Neither server has anything ftp related.

Actually, checking ftp on any IP reports either open or filtered, but always Host is up.

I'm guessing there is something in our network causing this effect, but I have no idea how would I actually find out, what is it. Please help.

Tymur Gubayev

Asked: 2021-10-21 04:39:30 +0800 CST

OpenBSD netcat times out depending on network interface

0

There is a network I'm accessing using PPTP VPN. I'm trying to setup something to monitor if the network is accessible, and email me if not. I've got a Raspberry Pi, it's connected to the network itself via WLAN and to a mobile router via Ethernet.

Just making sure I understand netcat correctly, I'm checking if I can connect to google, the idea being, should this work, I'll just substitute host and port with vpn address and 1723 (for PPTP) and it will just work.

Using default interface (wlan0) works.

$ nc -vz www.google.com 80
Connection to www.google.com 80 port [tcp/http] succeeded!

But using the ethernet (eth0) it doesn't work.

$ nc -vz -s 192.168.1.102 www.google.com 80
nc: connect to www.google.com port 80 (tcp) failed: Connection timed out
nc: getaddrinfo: Address family for hostname not supported

Same if I substitute www.google.com with ip.

$ nc -vz -s 192.168.1.102 172.217.168.68 80
nc: connect to 172.217.168.68 port 80 (tcp) failed: Connection timed out

But curl works:

$ curl --interface eth0 --head www.google.com
HTTP/1.1 200 OK
[more stuff]

curl ifconfig.me and curl --interface eth0 ifconfig.me show different IP addresses, so I am confident both interfaces have access to the internet, are working, and are different.

The netcat is OpenBSD netcat.

$ nc -h
OpenBSD netcat (Debian patchlevel 1.195-2)

The machine is a default raspberry pi, the only configuration I did was setting the interfaces up.

What is it that may prevent netcat from working on one of the interfaces?

UPDATE

A workaround I found is nmap:

$ nmap --version
Nmap version 7.70 ( https://nmap.org )

$ nmap -e eth0 -p pptp -Pn my.vpn.host | grep "open"

Tymur Gubayev

Asked: 2021-09-14 05:10:32 +0800 CST

Windows Server 2012 R2 - User Account Single App

1

I have a Windows Server 2012 R2 with multiple user accounts. One account ("test") is configured in such a way that on logon a program is started and when the program is closed the account is automatically logged out. This "test" account can log in via Remote Desktop or directly (the server is a Hyper-V machine). Other accounts behave normally.

I need to create a "test2" account with same properties and can't figure out how. As far as I can tell this is neither Kiosk-Mode, nor "Single App Terminal Server" and I'm completely lost. The server is also not part of any domain and it doesn't have Active Directory.

What could it be, where should I look?

UPDATE

It turns out, the app is set up as user shell (HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell), which I actually knew was a possibility - but searching the registry for the app name resulted in nothing, because HKEY_USERS doesn't have keys for every single user, only for the "actively loaded user profiles".

Tymur Gubayev

Asked: 2020-07-30 09:52:47 +0800 CST

L2TP over IPSec strongswan/xl2tpd pppd interface name changes

1

I have encountered a possible problem in my VPN setup. I have two different entry points into clients network, so I set two services up and, since one of the VPN-connections is slightly better for us, set it's metric to 100 and another to 101 like following.

/etc/ppp/ip-up.local

  metric=100
  if [[ $PPP_IFACE == 'ppp2' ]]; then
    metric=101;
    # ppp2 have lower priority
  fi;
  route add -net 10.20.0.0 netmask 255.255.0.0 dev $PPP_IFACE metric $metric

The interface names are set in /etc/ppp/*.options with unit 2 and unit 3:

ipcp-accept-local
ipcp-accept-remote
refuse-eap
require-chap
noccp
noauth
#noaccomp
mtu 1280
mru 1280
noipdefault
#defaultroute
nodefaultroute
#usepeerdns
unit 2
connect-delay 5000
name myname
password mypassword

Since I knew the names of the interfaces, I was lazy and just added fix rules to iptables and thought I was done with it (instead of adding/removing them in a script).

But then I saw an ppp0 interface...

Some research got me this.

sudo grep -iRn "pppd" /var/log/ give me this

/var/log/syslog:5697:Jul 29 10:55:58 debian-router pppd[5153]: LCP terminated by peer
/var/log/syslog:5698:Jul 29 10:55:58 debian-router pppd[5153]: Connect time 643.1 minutes.
/var/log/syslog:5699:Jul 29 10:55:58 debian-router pppd[5153]: Sent 0 bytes, received 0 bytes.
/var/log/syslog:5702:Jul 29 10:55:58 debian-router pppd[5153]: Overriding mtu 1500 to 1280
/var/log/syslog:5703:Jul 29 10:55:58 debian-router pppd[5153]: Overriding mru 1500 to mtu value 1280
/var/log/syslog:5707:Jul 29 10:55:58 debian-router xl2tpd[3016]: Terminating pppd: sending TERM signal to pid 5153
/var/log/syslog:5708:Jul 29 10:55:58 debian-router pppd[5153]: Terminating on signal 15
/var/log/syslog:5713:Jul 29 10:56:01 debian-router xl2tpd[3016]: start_pppd: I'm running:
/var/log/syslog:5714:Jul 29 10:56:01 debian-router xl2tpd[3016]: "/usr/sbin/pppd"
/var/log/syslog:5724:Jul 29 10:56:01 debian-router pppd[5613]: Plugin pppol2tp.so loaded.
/var/log/syslog:5725:Jul 29 10:56:01 debian-router pppd[5613]: pppd 2.4.7 started by root, uid 0
/var/log/syslog:5726:Jul 29 10:56:01 debian-router pppd[5613]: Couldn't allocate PPP unit 2 as it is already in use
/var/log/syslog:5727:Jul 29 10:56:01 debian-router pppd[5613]: Using interface ppp0
/var/log/syslog:5728:Jul 29 10:56:01 debian-router pppd[5613]: Connect: ppp0 <-->
/var/log/syslog:5729:Jul 29 10:56:01 debian-router pppd[5613]: Overriding mtu 1500 to 1280
/var/log/syslog:5730:Jul 29 10:56:01 debian-router pppd[5613]: Overriding mru 1500 to mtu value 1280
/var/log/syslog:5732:Jul 29 10:56:01 debian-router pppd[5613]: Overriding mtu 1500 to 1280
/var/log/syslog:5733:Jul 29 10:56:01 debian-router pppd[5613]: PAP authentication succeeded
/var/log/syslog:5734:Jul 29 10:56:01 debian-router pppd[5153]: Connection terminated.
/var/log/syslog:5736:Jul 29 10:56:01 debian-router pppd[5153]: Modem hangup
/var/log/syslog:5737:Jul 29 10:56:01 debian-router pppd[5153]: Exit.

So what happens must be... For some (probably irrelevant) reason the connection is terminated, upon which xl2tpd sends TERM to the pppd[5153] and then starts new pppd[5613] for the new connection. But pppd[5153] needs some time to exit and so pppd[5613] can't use designated interface name ppp2.

/etc/xl2tpd/xl2tpd.conf is like this.

[lac vpn1]
lns = 10.20.30.40
;ppp debug = yes
pppoptfile = /etc/ppp/options.vpn1.l2tpd
length bit = yes
redial = yes
redial timeout = 2
; max redials = 15

[lac vpn2]
lns = 10.20.30.41
;ppp debug = yes
pppoptfile = /etc/ppp/options.vpn2.l2tpd
length bit = yes
redial = yes
redial timeout = 2
; max redials = 15

Now, I guess I could set redial timeout in xl2tpd.conf higher, but it wouldn't be very clean solution to the problem. So the question is, is it possible to ensure device name is kept across reconnects? (If not I guess I could just use $PPP_REMOTE -- but not really, since it's not the lns = 10.20.30.41! -- in my ip-up.local instead of $PPP_IFACE and add/remove iptables rules there too, but maybe there is a better way).

Update I added ipparam vpn1 and ipparam vpn2 to the /etc/ppp/*.options files and use $PPP_IPPARAM to distinguish between the two; I guess this is the most stable solution.

Additional info:

OS: Debian GNU/Linux 10 (buster)
ipsec: Linux strongSwan U5.7.2/K4.19.0-9-amd64
xl2tpd: xl2tpd-1.3.12

Tymur Gubayev

Asked: 2020-07-25 09:16:15 +0800 CST

L2TP over IPSec strongswan/xl2tpd works on clone but not on original

0

I'm setting up VPN connection from firm network to clients. Currently: L2TP VPN. My first step was cloning current router-VM (it's a Hyper-V machine). I then proceeded to configure and experiment with the clone. Once I got the result I wanted, I redid necessary steps on the original. The setup is now identical (beside IP-Address). But for some reason only the clone can connect (and does so consistently), while the original fails almost always -- but did connect once for some reason.

The setup is like this.

OS: Debian GNU/Linux 10 (buster)
ipsec: Linux strongSwan U5.7.2/K4.19.0-9-amd64
xl2tpd: xl2tpd-1.3.12

/etc/ipsec.conf

conn %default
  ikelifetime=60m
  keylife=20m
  rekeymargin=3m
  keyingtries=1
  keyexchange=ikev1
  authby=secret
  ike=3des-sha1-modp1024
  esp=3des-sha1-modp1024

conn vpnTheClient
  keyexchange=ikev1
  left=%defaultroute
  auto=add
  authby=secret
  type=transport
  leftprotoport=17/%any
  rightprotoport=17/%any
  right=10.20.30.40

/etc/ipsec.secrets

  %any 10.20.30.40 : PSK "somestrongstring"

/etc/xl2tpd/xl2tpd.conf

[global]
debug tunnel = yes
debug avp = yes
debug network = yes
debug packet = yes
debug state = yes

[lac vpnTheClient]
lns = 10.20.30.40
ppp debug = yes
pppoptfile = /etc/ppp/options.TheClient.l2tpd
length bit = yes

/etc/ppp/options.TheClient.l2tpd

ipcp-accept-local
ipcp-accept-remote
refuse-eap
require-chap
noccp
noauth
noaccomp
mtu 1280
mru 1280
noipdefault
#defaultroute
nodefaultroute
#usepeerdns
unit 3
connect-delay 5000
name vpnusername
password vpnPasswrd!

Now I do sudo xl2tpd -D from one session and sudo /bin/sh -c 'echo "c vpnTheClient" > /var/run/xl2tpd/l2tp-control' from another.

The original one first failed try looks like following.

xl2tpd[11360]: Not looking for kernel SAref support.
xl2tpd[11360]: Using l2tp kernel support.
xl2tpd[11360]: xl2tpd version xl2tpd-1.3.12 started on debian-router PID:11360
xl2tpd[11360]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc.
xl2tpd[11360]: Forked by Scott Balmos and David Stipp, (C) 2001
xl2tpd[11360]: Inherited by Jeff McAdams, (C) 2002
xl2tpd[11360]: Forked again by Xelerance (www.xelerance.com) (C) 2006-2016
xl2tpd[11360]: Listening on IP address 0.0.0.0, port 1701
xl2tpd[11360]: get_call: allocating new tunnel for host 10.20.30.40, port 1701.
xl2tpd[11360]: Connecting to host 10.20.30.40, port 1701
xl2tpd[11360]: control_finish: message type is (null)(0).  Tunnel is 0, call is 0.
packet dump:
HEX: { C8 02 00 6E 00 00 00 00 00 00 00 00 80 08 00 00 00 00 00 01 80 08 00 00 00 02 01 00 80 0A 00 00 00 03 00 00 00 03 80 0A 00 00 00 04 00 00 00 00 00 08 00 00 00 06 06 90 80 13 00 00 00 07 64 65 62 69 61 6E 2D 72 6F 75 74 65 72 00 13 00 00 00 08 78 65 6C 65 72 61 6E 63 65 2E 63 6F 6D 80 08 00 00 00 09 47 7A 80 08 00 00 00 0A 00 04 }
ASCII: {    n                                                          debian-router      xelerance.com      Gz        }
xl2tpd[11360]: control_finish: sending SCCRQ
xl2tpd[11360]: network_thread: select timeout with max retries: 5 for tunnel: 18298
xl2tpd[11360]: network_thread: select timeout with max retries: 5 for tunnel: 18298
xl2tpd[11360]: network_thread: select timeout with max retries: 5 for tunnel: 18298
xl2tpd[11360]: network_thread: select timeout with max retries: 5 for tunnel: 18298
xl2tpd[11360]: network_thread: select timeout with max retries: 5 for tunnel: 18298
xl2tpd[11360]: Maximum retries exceeded for tunnel 18298.  Closing.

Now from clone, the very same settings:

xl2tpd[2299]: Not looking for kernel SAref support.
xl2tpd[2299]: Using l2tp kernel support.
xl2tpd[2299]: xl2tpd version xl2tpd-1.3.12 started on debian-router-copy PID:2299
xl2tpd[2299]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc.
xl2tpd[2299]: Forked by Scott Balmos and David Stipp, (C) 2001
xl2tpd[2299]: Inherited by Jeff McAdams, (C) 2002
xl2tpd[2299]: Forked again by Xelerance (www.xelerance.com) (C) 2006-2016
xl2tpd[2299]: Listening on IP address 0.0.0.0, port 1701
xl2tpd[2299]: get_call: allocating new tunnel for host 10.20.30.40, port 1701.
xl2tpd[2299]: Connecting to host 10.20.30.40, port 1701
xl2tpd[2299]: control_finish: message type is (null)(0).  Tunnel is 0, call is 0.
packet dump:
HEX: { C8 02 00 73 00 00 00 00 00 00 00 00 80 08 00 00 00 00 00 01 80 08 00 00 00 02 01 00 80 0A 00 00 00 03 00 00 00 03 80 0A 00 00 00 04 00 00 00 00 00 08 00 00 00 06 06 90 80 18 00 00 00 07 64 65 62 69 61 6E 2D 72 6F 75 74 65 72 2D 63 6F 70 79 00 13 00 00 00 08 78 65 6C 65 72 61 6E 63 65 2E 63 6F 6D 80 08 00 00 00 09 9C 82 80 08 00 00 00 0A 00 04 }
ASCII: {    s                                                          debian-router-copy      xelerance.com
}
xl2tpd[2299]: control_finish: sending SCCRQ
xl2tpd[2299]: network_thread: recv packet from 10.20.30.40, size = 96, tunnel = 40066, call = 0 ref=0 refhim=0
packet dump:
  <etc now everything is working>

Then I tried adding noaccomp to the options, and all of a sudden the original worked.

xl2tpd[11881]: Not looking for kernel SAref support.
xl2tpd[11881]: Using l2tp kernel support.
xl2tpd[11881]: xl2tpd version xl2tpd-1.3.12 started on debian-router PID:11881
xl2tpd[11881]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc.
xl2tpd[11881]: Forked by Scott Balmos and David Stipp, (C) 2001
xl2tpd[11881]: Inherited by Jeff McAdams, (C) 2002
xl2tpd[11881]: Forked again by Xelerance (www.xelerance.com) (C) 2006-2016
xl2tpd[11881]: Listening on IP address 0.0.0.0, port 1701
xl2tpd[11881]: get_call: allocating new tunnel for host 10.20.30.40, port 1701.
xl2tpd[11881]: Connecting to host 10.20.30.40, port 1701
xl2tpd[11881]: control_finish: message type is (null)(0).  Tunnel is 0, call is 0.
packet dump:
HEX: { C8 02 00 6E 00 00 00 00 00 00 00 00 80 08 00 00 00 00 00 01 80 08 00 00 00 02 01 00 80 0A 00 00 00 03 00 00 00 03 80 0A 00 00 00 04 00 00 00 00 00 08 00 00 00 06 06 90 80 13 00 00 00 07 64 65 62 69 61 6E 2D 72 6F 75 74 65 72 00 13 00 00 00 08 78 65 6C 65 72 61 6E 63 65 2E 63 6F 6D 80 08 00 00 00 09 64 83 80 08 00 00 00 0A 00 04 }
ASCII: {    n                                                          debian-router      xelerance.com      d         }
xl2tpd[11881]: control_finish: sending SCCRQ
xl2tpd[11881]: network_thread: recv packet from 10.20.30.40, size = 96, tunnel = 25731, call = 0 ref=0 refhim=0
packet dump:
  <etc now everything is working>

But only this one time.

Question: how do I debug this thing (I'm only very novice Linux user)? What could possibly be the reason for this? I want to accentuate, the clone has never had any issues connecting -- with exact same config as far as I am aware.

Tymur Gubayev

Asked: 2020-05-13 06:28:47 +0800 CST

A route between networks stopped working

1

Small introduction: I recently inherited network administrator role in a small firm, because my colleague died unexpectedly. I'm a programmer and have some very shallow knowledge about how networks are working, so please forgive me in advance for too much/little/nonsensical information in this question.

On a windows server in our network are 2 Hyper-V machines running, let's call them Router-A and Router-B. Both have Windows 10 Enterprise as OS and using Palo Alto GlobalProtect (although different versions) to establish VPN connection into clients' networks.

Client A asked me to restart the VPN connection, due to some weirdness of the GlobalProtect version I decided to restart the whole Virtual PC.

After that, when Router-A was up again I checked the VPN from inside of Router-A -- it was working. Client was happy.

Unfortunately, trying to ping a valid IP address in the A network from host machine didn't work. A ping into B network did still work.

And now (after some hours of searching and experimenting) I'm asking for help.

Network info:

our subnetwork: 147.44.7.0/24
client A: router: 147.44.7.6; IP: 192.168.101.0/24
client B: router: 147.44.7.7; IP: 172.20.5.0/24

On host machine (sry, OS language is German):

C:\Users\myuser>route print -4
===========================================================================
Schnittstellenliste
 46...........................RAS (Dial In) Interface
 27...2c 76 8a 4e f2 79 ......Hyper-V-Adapter - virtuelles Ethernet #2
  1...........................Software Loopback Interface 1
 18...00 00 00 00 00 00 00 e0 Microsoft-ISATAP-Adapter #2
 22...00 00 00 00 00 00 00 e0 Microsoft-ISATAP-Adapter #4
 24...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface
===========================================================================

IPv4-Routentabelle
===========================================================================
Aktive Routen:
     Netzwerkziel    Netzwerkmaske          Gateway    Schnittstelle Metrik
          0.0.0.0          0.0.0.0       147.44.7.9       147.44.7.1    261
         10.8.0.0      255.255.0.0      147.44.7.65       147.44.7.1      6
        127.0.0.0        255.0.0.0   Auf Verbindung         127.0.0.1    306
        127.0.0.1  255.255.255.255   Auf Verbindung         127.0.0.1    306
  127.255.255.255  255.255.255.255   Auf Verbindung         127.0.0.1    306
       147.44.7.0    255.255.255.0   Auf Verbindung        147.44.7.1    261
       147.44.7.1  255.255.255.255   Auf Verbindung        147.44.7.1    261
      147.44.7.28  255.255.255.255      147.44.7.28      147.44.7.90     24
      147.44.7.34  255.255.255.255      147.44.7.34      147.44.7.90     24
      147.44.7.90  255.255.255.255   Auf Verbindung       147.44.7.90    279
     147.44.7.255  255.255.255.255   Auf Verbindung        147.44.7.1    261
       172.20.5.0    255.255.255.0       147.44.7.7       147.44.7.1      6
    192.168.101.0    255.255.255.0       147.44.7.6       147.44.7.1      6
        224.0.0.0        240.0.0.0   Auf Verbindung         127.0.0.1    306
        224.0.0.0        240.0.0.0   Auf Verbindung        147.44.7.1    261
        224.0.0.0        240.0.0.0   Auf Verbindung       147.44.7.90    279
  255.255.255.255  255.255.255.255   Auf Verbindung         127.0.0.1    306
  255.255.255.255  255.255.255.255   Auf Verbindung        147.44.7.1    261
  255.255.255.255  255.255.255.255   Auf Verbindung       147.44.7.90    279
===========================================================================
Ständige Routen:
  Netzwerkadresse          Netzmaske  Gatewayadresse  Metrik
          0.0.0.0          0.0.0.0       147.44.7.9  Standard
       172.20.5.0    255.255.255.0       147.44.7.7       1
         10.8.0.0      255.255.0.0      147.44.7.65       1
          0.0.0.0          0.0.0.0       147.44.7.9     256
    192.168.101.0    255.255.255.0       147.44.7.6       1
===========================================================================

C:\Users\myuser>tracert 172.20.5.132

Routenverfolgung zu 172.20.5.132 über maximal 30 Hops

  1    <1 ms     *       <1 ms  wmsrv08-11.mycompany.de [147.44.7.7]
  2     *        *        *     Zeitüberschreitung der Anforderung.
  3    24 ms    30 ms    21 ms  192.168.82.1
  4    31 ms    32 ms    23 ms  172.20.5.132

Ablaufverfolgung beendet.

C:\Users\myuser>tracert 192.168.101.137

Routenverfolgung zu 192.168.101.137 über maximal 30 Hops

  1     *        *        *     Zeitüberschreitung der Anforderung.
  2     *        *        *     Zeitüberschreitung der Anforderung.
  3     *        *        *     Zeitüberschreitung der Anforderung.
  4     *        *        *     Zeitüberschreitung der Anforderung.
  5     *        *        *     Zeitüberschreitung der Anforderung.
  6     *        *        *     Zeitüberschreitung der Anforderung.
  7     *        *        *     Zeitüberschreitung der Anforderung.
  8     *        *        *     Zeitüberschreitung der Anforderung.
  9     *        *        *     Zeitüberschreitung der Anforderung.
 10     *        *        *     Zeitüberschreitung der Anforderung.
 11     *        *        *     Zeitüberschreitung der Anforderung.
 12     *        *        *     Zeitüberschreitung der Anforderung.
 13     *        *        *     Zeitüberschreitung der Anforderung.
 14     *        *        *     Zeitüberschreitung der Anforderung.
 15     *        *        *     Zeitüberschreitung der Anforderung.
 16     *        *        *     Zeitüberschreitung der Anforderung.
 17     *        *        *     Zeitüberschreitung der Anforderung.
 18     *     ^C
C:\Users\myuser>

ping to neither of routers works.

From inside Router-A:

C:\Users\VPN>tracert 192.168.101.137

Routenverfolgung zu redacted_clientA_name.intern [192.168.101.137] über maximal 30 Hops: 

1    26 ms     28 ms     24 ms     192.168.171.129
2    24 ms     47 ms     23 ms     192.168.235.2
3    25 ms     24 ms     24 ms     redacted_clientA_name.intern [192.168.101.137] 

Üblaufverfolgung beendet.

C:\Users\VPN>ipconfig /all

Windows-IP-Konfiguration

Hostname . . . . . . . . . . . . : wmsrv08-10
Primäres DNS-Suffix . . . . . . . : mycompany.de
Knotentyp . . . . . . . . . . . . : Hybrid
IP-Routing aktiviert . . . . . . : Nein
WINS-Proxy aktiviert . . . . . . : Nein
DNS-Suffixsuchliste . . . . . . . : mycompany.de

Ethernet-Adapter Ethernet 8:

Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : PANGP Virtual Ethernet Adapter #7
Physische Adresse . . . . . . . . : 02-50-41-00-00-01
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja
IPv4-Adresse . . . . . . . . . . : 192.168.171.153(Bevorzugt)
Subnetzmaske . . . . . . . . . . : 255.255.255.255
Standardgateway . . . . . . . . . : 0.0.0.0
DHCPv6-IAID . . . . . . . . . . . : 184700993
DHCPv6-Client-DUID. . . . . . . . : 00-01-00-01-1F-27-7E-FF-00-15-5D-07-01-11
DNS-Server . . . . . . . . . . . : 192.168.101.163
192.168.101.164
NetBIOS über TCP/IP . . . . . . . : Aktiviert

Ethernet-Adapter Ethernet:

Verbindungsspezifisches DNS-Suffix: 
Beschreibung. . . . . . . . . . . : Microsoft Hyper-V Network Adapter
Physische Adresse . . . . . . . . : 00-15-5D-07-01-11
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja
Verbindungslokale IPv6-Adresse . : fe80::519e:598f:9505:2c8a%16(Bevorzugt)
IPv4-Adresse . . . . . . . . . . : 147.44.7.6(Bevorzugt)
Subnetzmaske . . . . . . . . . . : 255.255.255.0
Standardgateway . . . . . . . . . : 147.44.7.9
DHCPv6-IAID . . . . . . . . . . . : 50337117
DHCPv6-Client-DUID. . . . . . . . : 00-01-00-01-1F-27-7E-FF-00-15-5D-07-01-11
DNS-Server . . . . . . . . . . . : 147.44.7.1
147.44.7.22
NetBIOS über TCP/IP . . . . . . . : Aktiviert

From inside Router-B:

C:\Users\VPN>tracert 172.20.5.132

Routenverfolgung zu redacted_clientB_name.de [172.20.5.132] über maximal 30 Hops: 

1    21 ms     35 ms     20 ms     192.168.82.1
2    24 ms     32 ms     21 ms     redacted_clientB_name.de [172.20.5.132] 

Üblaufverfolgung beendet.

C:\Users\VPN>ipconfig -all

Windows-IP-Konfiguration

Hostname . . . . . . . . . . . . : wmsrv08-11
Primäres DNS-Suffix . . . . . . . : wmdom03.mycompany.de
Knotentyp . . . . . . . . . . . . : Hybrid
IP-Routing aktiviert . . . . . . : Nein
WINS-Proxy aktiviert . . . . . . : Nein
DNS-Suffixsuchliste . . . . . . . : redacted_clientB_name1.de
redacted_clientB_name2.com
redacted_clientB_name3.com
wmdom03.mycompany.de

Ethernet-Adapter Ethernet 6:

Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : PANGP Virtual Ethernet Adapter #5
Physische Adresse . . . . . . . . : 02-50-41-00-00-01
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja
Verbindungslokale IPv6-Adresse . : fe80::6813:ec02:5ae6:9926%8(Bevorzugt)
IPv4-Adresse . . . . . . . . . . : 192.168.82.104(Bevorzugt)
Subnetzmaske . . . . . . . . . . : 255.255.255.255
Standardgateway . . . . . . . . . :
DHCPv6-IAID . . . . . . . . . . . : 235032641
DHCPv6-Client-DUID. . . . . . . . : 00-01-00-01-20-4E-EA-29-00-15-5D-07-01-12
DNS-Server . . . . . . . . . . . : 144.4.190.35
144.4.190.34
NetBIOS über TCP/IP . . . . . . . : Aktiviert

Ethernet-Adapter Ethernet:

Verbindungsspezifisches DNS-Suffix: wmdom03.mycompany.de
Beschreibung. . . . . . . . . . . : Microsoft Hyper-V Network Adapter
Physische Adresse . . . . . . . . : 00-15-5D-07-01-12
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja
Verbindungslokale IPv6-Adresse . : fe80::88d1:57f4:209c:943a%10(Bevorzugt)
IPv4-Adresse . . . . . . . . . . : 147.44.7.7(Bevorzugt)
Subnetzmaske . . . . . . . . . . : 255.255.255.0
Standardgateway . . . . . . . . . : 147.44.7.9
DHCPv6-IAID . . . . . . . . . . . : 50337117
DHCPv6-Client-DUID. . . . . . . . : 00-01-00-01-20-4E-EA-29-00-15-5D-07-01-12
DNS-Server . . . . . . . . . . . : fd3f:a1ac:46f3:1::1
fd3f:a1ac:46f3:1::3
147.44.7.1
147.44.7.22
NetBIOS über TCP/IP . . . . . . . : Aktiviert
Suchliste für verbindungsspezifische DNS-Suffixe:
wmdom03.mycompany.de

ipconfig on host:

C:\Windows\system32>ipconfig /all

Windows-IP-Konfiguration

Hostname . . . . . . . . . . . . : wmsrv08
Primäres DNS-Suffix . . . . . . . : wmdom03.mycompany.de
Knotentyp . . . . . . . . . . . . : Hybrid
IP-Routing aktiviert . . . . . . : Ja
WINS-Proxy aktiviert . . . . . . : Nein
DNS-Suffixsuchliste . . . . . . . : wmdom03.mycompany.de

PPP-Adapter RAS (Dial In) Interface:

Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : RAS (Dial In) Interface
Physische Adresse . . . . . . . . :
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja
IPv4-Adresse . . . . . . . . . . : 147.44.7.90(Bevorzugt)
Subnetzmaske . . . . . . . . . . : 255.255.255.255
Standardgateway . . . . . . . . . :
NetBIOS über TCP/IP . . . . . . . : Aktiviert

Ethernet-Adapter vEthernet (Intranet):

Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : Hyper-V-Adapter - virtuelles Ethernet #2
Physische Adresse . . . . . . . . : 2C-76-8A-4E-F2-79
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja
IPv6-Adresse. . . . . . . . . . . : fd3f:a1ac:46f3:1::1(Bevorzugt)
Verbindungslokale IPv6-Adresse . : fe80::58c9:5b1d:1ee8:dc48%27(Bevorzugt)
IPv4-Adresse . . . . . . . . . . : 147.44.7.1(Bevorzugt)
Subnetzmaske . . . . . . . . . . : 255.255.255.0
Standardgateway . . . . . . . . . : 147.44.7.9
DHCPv6-IAID . . . . . . . . . . . : 657225354
DHCPv6-Client-DUID. . . . . . . . : 00-01-00-01-18-06-CD-D6-2C-76-8A-4E-F2-78

DNS-Server . . . . . . . . . . . : ::1
fd3f:a1ac:46f3:1::3
127.0.0.1
147.44.7.22
NetBIOS über TCP/IP . . . . . . . : Deaktiviert

Tunneladapter isatap.{6E06F030-7526-11D2-BAF4-00600815A4BD}:

Medienstatus. . . . . . . . . . . : Medium getrennt
Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : Microsoft-ISATAP-Adapter #2
Physische Adresse . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja

Tunneladapter isatap.{EABE234A-7FED-4815-B40F-E87C6BDD4EE3}:

Medienstatus. . . . . . . . . . . : Medium getrennt
Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : Microsoft-ISATAP-Adapter #4
Physische Adresse . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja

Tunneladapter Teredo Tunneling Pseudo-Interface:

Medienstatus. . . . . . . . . . . : Medium getrennt
Verbindungsspezifisches DNS-Suffix:
Beschreibung. . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
Physische Adresse . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP aktiviert. . . . . . . . . . : Nein
Autokonfiguration aktiviert . . . : Ja

Can someone help me? Is this even the right place for this kind of questions (sry if not)?

Till now the only differences I see between the 2 routers is following.

The DNS-Searchlist in router-B has 4 entries, last one "wmdom03.mycompany.de", and this suffix is also seen as "Connectionspecific DNS-Suffix" in ipconfig /all; in router-A, the search list only has a single entry -- "wmdom03.mycompany.de", and "Connectionspecific DNS-Suffix" stays empty unless I set the "DNS-Suffix for this connection" explicitly.
Both router-A and -B have IPv6 enabled and set to discover DNS-Serveraddress automatically, but only router-B got them.

UPDATE1: add ipconfig /all for the 3 relevant systems. UPDATE2: add discovered differences between router

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