Problem
You can not reach you local UCS host from within the LAN. From the Internet access works fine.
Investigation
The server can not be reached by any tools. But all services (mail, ssh, …) can be used when trying to connect from external Internet (through a port forwarding router) or through the configured OpenVPN connection.
Using “ping” from the local network it does not get any replies:
root@any:~# ping ucs
PING ucs.multi.ucs (192.168.19.100) 56(84) bytes of data.
^C
--- ucs.multi.ucs ping statistics ---
5 packets transmitted, 0 received, +3 errors, 100% packet loss, time 4101ms
pipe 4
The “arp” command afterwards shows the correct IP <-> MAC mapping but can not resolve the hostname:
? (192.168.19.100) at 00:1a:8c:13:aa:87 [ether] at eth1
From within the UCS host you are not able to ping any host- not even the above mentioned router.
The routing tables shows:
root@ucs:~# route -n
Kernel-IP-Routingtable
Ziel Router Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.19.1 0.0.0.0 UG 0 0 0 eth1
172.17.0.0 0.0.0.0 255.255.0.0 U 0 0 0 docker0
192.168.9.0 10.20.30.1 255.255.255.0 U 0 0 0 tun0
192.168.9.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
So all packets for the local network were sent out through the OpenVPN interface and thus never reached the loccal network.
Solution
The OpenVPN app was misconfigured. In the file /etc/openvpn/server.conf remove (or comment out) the following entry:
route 192.168.9.0 255.255.255.0 10.20.30.1
Then delete the local route:
ip route del 192.168.19.0/24 via 10.20.30.1 dev tun0
And restart OpenVPN service.
Afterwards, check you OpenVPN configuration in UMC which caused the invalid routing entry.