Ubuntu 20.04 server unreachable from external world

Question

i have an Ubuntu server where i can not access the server from external machines. I have tried to ssh to the Ubuntu machine but it seams that all requests are drooped or does not arrive. I have not set any special routing or ip configuration.

The subnet looks like this:

        router
           |
  ---------+--------------------
  |        |         |         |
Ubuntu  raspberry  raspberry raspberry

Firstly i enter in the network via a vpn, and after that i want to log in to my Ubuntu machine but i can not do that, so i tried to access the raspberries and when i saw that i can enter to the raspberries i tried to ssh to my Ubuntu server from the raspberries, and it worked.

From the router i see all of the machines.

Anybody can help me access my Ubuntu server without accessing fist one of the raspberries?

sudo iptables-save

# Generated by iptables-save v1.8.4 on Fri Sep 11 07:58:24 2020
*nat
:PREROUTING ACCEPT [60337:4082282]
:INPUT ACCEPT [5:300]
:OUTPUT ACCEPT [4920:342818]
:POSTROUTING ACCEPT [4920:342818]
:OUTPUT_direct - [0:0]
:POSTROUTING_ZONES - [0:0]
:POSTROUTING_direct - [0:0]
:POST_public - [0:0]
:POST_public_allow - [0:0]
:POST_public_deny - [0:0]
:POST_public_log - [0:0]
:POST_public_post - [0:0]
:POST_public_pre - [0:0]
:PREROUTING_ZONES - [0:0]
:PREROUTING_direct - [0:0]
:PRE_public - [0:0]
:PRE_public_allow - [0:0]
:PRE_public_deny - [0:0]
:PRE_public_log - [0:0]
:PRE_public_post - [0:0]
:PRE_public_pre - [0:0]
-A PREROUTING -j PREROUTING_direct
-A PREROUTING -j PREROUTING_ZONES
-A OUTPUT -j OUTPUT_direct
-A POSTROUTING -j POSTROUTING_direct
-A POSTROUTING -j POSTROUTING_ZONES
-A POSTROUTING_ZONES -o eno1 -g POST_public
-A POSTROUTING_ZONES -g POST_public
-A POST_public -j POST_public_pre
-A POST_public -j POST_public_log
-A POST_public -j POST_public_deny
-A POST_public -j POST_public_allow
-A POST_public -j POST_public_post
-A PREROUTING_ZONES -i eno1 -g PRE_public
-A PREROUTING_ZONES -g PRE_public
-A PRE_public -j PRE_public_pre
-A PRE_public -j PRE_public_log
-A PRE_public -j PRE_public_deny
-A PRE_public -j PRE_public_allow
-A PRE_public -j PRE_public_post
COMMIT
# Completed on Fri Sep 11 07:58:24 2020
# Generated by iptables-save v1.8.4 on Fri Sep 11 07:58:24 2020
*mangle
:PREROUTING ACCEPT [78641:5937844]
:INPUT ACCEPT [78611:5935350]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [46644:3913664]
:POSTROUTING ACCEPT [46670:3916660]
:FORWARD_direct - [0:0]
:INPUT_direct - [0:0]
:OUTPUT_direct - [0:0]
:POSTROUTING_direct - [0:0]
:PREROUTING_ZONES - [0:0]
:PREROUTING_direct - [0:0]
:PRE_public - [0:0]
:PRE_public_allow - [0:0]
:PRE_public_deny - [0:0]
:PRE_public_log - [0:0]
:PRE_public_post - [0:0]
:PRE_public_pre - [0:0]
-A PREROUTING -j PREROUTING_direct
-A PREROUTING -j PREROUTING_ZONES
-A INPUT -j INPUT_direct
-A FORWARD -j FORWARD_direct
-A OUTPUT -j OUTPUT_direct
-A POSTROUTING -j POSTROUTING_direct
-A PREROUTING_ZONES -i eno1 -g PRE_public
-A PREROUTING_ZONES -g PRE_public
-A PRE_public -j PRE_public_pre
-A PRE_public -j PRE_public_log
-A PRE_public -j PRE_public_deny
-A PRE_public -j PRE_public_allow
-A PRE_public -j PRE_public_post
COMMIT
# Completed on Fri Sep 11 07:58:24 2020
# Generated by iptables-save v1.8.4 on Fri Sep 11 07:58:24 2020
*raw
:PREROUTING ACCEPT [78642:5937896]
:OUTPUT ACCEPT [46646:3914420]
:OUTPUT_direct - [0:0]
:PREROUTING_ZONES - [0:0]
:PREROUTING_direct - [0:0]
:PRE_public - [0:0]
:PRE_public_allow - [0:0]
:PRE_public_deny - [0:0]
:PRE_public_log - [0:0]
:PRE_public_post - [0:0]
:PRE_public_pre - [0:0]
-A PREROUTING -j PREROUTING_direct
-A PREROUTING -j PREROUTING_ZONES
-A OUTPUT -j OUTPUT_direct
-A PREROUTING_ZONES -i eno1 -g PRE_public
-A PREROUTING_ZONES -g PRE_public
-A PRE_public -j PRE_public_pre
-A PRE_public -j PRE_public_log
-A PRE_public -j PRE_public_deny
-A PRE_public -j PRE_public_allow
-A PRE_public -j PRE_public_post
COMMIT
# Completed on Fri Sep 11 07:58:24 2020
# Generated by iptables-save v1.8.4 on Fri Sep 11 07:58:24 2020
*security
:INPUT ACCEPT [19038:1906726]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [47400:3969196]
:FORWARD_direct - [0:0]
:INPUT_direct - [0:0]
:OUTPUT_direct - [0:0]
-A INPUT -j INPUT_direct
-A FORWARD -j FORWARD_direct
-A OUTPUT -j OUTPUT_direct
COMMIT
# Completed on Fri Sep 11 07:58:24 2020
# Generated by iptables-save v1.8.4 on Fri Sep 11 07:58:24 2020
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [30649:2765745]
:FORWARD_IN_ZONES - [0:0]
:FORWARD_OUT_ZONES - [0:0]
:FORWARD_direct - [0:0]
:FWDI_public - [0:0]
:FWDI_public_allow - [0:0]
:FWDI_public_deny - [0:0]
:FWDI_public_log - [0:0]
:FWDI_public_post - [0:0]
:FWDI_public_pre - [0:0]
:FWDO_public - [0:0]
:FWDO_public_allow - [0:0]
:FWDO_public_deny - [0:0]
:FWDO_public_log - [0:0]
:FWDO_public_post - [0:0]
:FWDO_public_pre - [0:0]
:INPUT_ZONES - [0:0]
:INPUT_direct - [0:0]
:IN_public - [0:0]
:IN_public_allow - [0:0]
:IN_public_deny - [0:0]
:IN_public_log - [0:0]
:IN_public_post - [0:0]
:IN_public_pre - [0:0]
:OUTPUT_direct - [0:0]
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED,DNAT -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -j INPUT_direct
-A INPUT -j INPUT_ZONES
-A INPUT -m conntrack --ctstate INVALID -j DROP
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED,DNAT -j ACCEPT
-A FORWARD -i lo -j ACCEPT
-A FORWARD -j FORWARD_direct
-A FORWARD -j FORWARD_IN_ZONES
-A FORWARD -j FORWARD_OUT_ZONES
-A FORWARD -m conntrack --ctstate INVALID -j DROP
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
-A OUTPUT -o lo -j ACCEPT
-A OUTPUT -j OUTPUT_direct
-A FORWARD_IN_ZONES -i eno1 -g FWDI_public
-A FORWARD_IN_ZONES -g FWDI_public
-A FORWARD_OUT_ZONES -o eno1 -g FWDO_public
-A FORWARD_OUT_ZONES -g FWDO_public
-A FWDI_public -j FWDI_public_pre
-A FWDI_public -j FWDI_public_log
-A FWDI_public -j FWDI_public_deny
-A FWDI_public -j FWDI_public_allow
-A FWDI_public -j FWDI_public_post
-A FWDI_public -p icmp -j ACCEPT
-A FWDO_public -j FWDO_public_pre
-A FWDO_public -j FWDO_public_log
-A FWDO_public -j FWDO_public_deny
-A FWDO_public -j FWDO_public_allow
-A FWDO_public -j FWDO_public_post
-A INPUT_ZONES -i eno1 -g IN_public
-A INPUT_ZONES -g IN_public
-A IN_public -j IN_public_pre
-A IN_public -j IN_public_log
-A IN_public -j IN_public_deny
-A IN_public -j IN_public_allow
-A IN_public -j IN_public_post
-A IN_public -p icmp -j ACCEPT
-A IN_public_allow -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW,UNTRACKED -j ACCEPT
COMMIT
# Completed on Fri Sep 11 07:58:24 2020

image of the ssh call

Can you post the output of the `ssh` command you are trying to use to connect, preferably adding the `-v` option? — Bert, Sep 11 '20 at 14:25
@Bert i have attached the image, the ip, port and username has been cut out, but everything else is on the image. Btw the router sees the ubuntu machine — Balázs Dyntell, Sep 17 '20 at 06:29

score 0 · Accepted Answer · answered Sep 17 '20 at 09:47

i have resolved the problem, with modifying the /etc/netplan/01-network-all.yaml file to the folloving:

network:
  version: 2
  renderer: networkd
  ethernets:
    eno1:
      addresses:
        - local ip/24
      gateway4: gateway ip
      nameservers:
        addresses:
          - 8.8.8.8
          - 8.8.4.4

after that i have runned the following commands:

sudo netplan --debug generate
sudo netplan apply
reboot

Ubuntu 20.04 server unreachable from external world

sudo iptables-save

1 Answers1