Unable to reach computer in same network

Question

Assume two machines that connect to a wireless router (Archer C7 v2) and are part of the same LAN. Pinging machine A from machine B works, but ssh, telnet, netcat fail. Why?

Details

Machine A (server running Ubuntu 14.04.5, local address 192.168.0.16)

An openssh server instance is up, listening at port 2200 and running w/o issues.

$netstat -ntlp | grep LISTEN
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:8979          0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      -               
tcp        0      0 0.0.0.0:2200            0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:29754         0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:10555         0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:1023          0.0.0.0:*               LISTEN      -               
tcp6       0      0 :::80                   :::*                    LISTEN      -               
tcp6       0      0 ::1:53                  :::*                    LISTEN      -               
tcp6       0      0 ::1:631                 :::*                    LISTEN      -               
tcp6       0      0 :::2200                 :::*                    LISTEN      -               

The firewall is disabled:

$sudo ufw status' gives
Status: inactive

This is the output of iptables -S as requested:

$iptables -S
-P INPUT DROP
-P FORWARD DROP
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-ISOLATION
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p udp -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i ipsec+ -p 254 -j ACCEPT
-A INPUT -p esp -j ACCEPT
-A INPUT -p ah -j ACCEPT
-A INPUT -p udp -m udp --dport 500 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5308 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5900 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5901 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 12080 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 113 -j REJECT --reject-with icmp-port-unreachable
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5656 -j ACCEPT
-A INPUT -p udp -m udp --dport 5004:5005 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5004:5005 -j ACCEPT
-A INPUT -p udp -m udp --dport 20830 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 20830 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5060:5062 -j ACCEPT
-A INPUT -p udp -m udp --dport 5060:5062 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 21100 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 2001 -j ACCEPT
-A INPUT -p gre -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 3 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 4 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 11 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 12 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 9 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 0 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 8081 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 1533 -j ACCEPT
-A INPUT -p udp -m state --state NEW -m udp --dport 52311 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 30000:30005 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 67:68 -j DROP
-A INPUT -p udp -m udp --dport 67:68 -j DROP
-A INPUT -p tcp -m tcp --dport 137 -j DROP
-A INPUT -p udp -m udp --dport 137 -j DROP
-A INPUT -p tcp -m tcp --dport 138 -j DROP
-A INPUT -p udp -m udp --dport 138 -j DROP
-A INPUT -p tcp -m tcp --dport 139 -j DROP
-A INPUT -p udp -m udp --dport 139 -j DROP
-A INPUT -p tcp -m tcp --dport 1:20 -j DROP
-A INPUT -p tcp -m tcp --dport 111 -j DROP
-A INPUT -p tcp -m tcp --dport 161:162 -j DROP
-A INPUT -p tcp -m tcp --dport 520 -j DROP
-A INPUT -p tcp -m tcp --dport 6348:6349 -j DROP
-A INPUT -p tcp -m tcp --dport 6345:6347 -j DROP
-A INPUT -p tcp -m limit --limit 3/min -j LOG --log-prefix "FIREWALL: " --log-level 7
-A INPUT -p udp -m limit --limit 3/min -j LOG --log-prefix "FIREWALL: " --log-level 7
-A INPUT -j DROP
-A FORWARD -j DOCKER-ISOLATION
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A DOCKER-ISOLATION -j RETURN

Machine B (client running macOS 10.12.6, local address 192.168.0.14)

Attempting to connect via ssh results in an "Operation timed out message":

$ssh user@192.168.0.16 -p 2200 -i ~/.ssh/id_rsa -vvv
OpenSSH_7.4p1, LibreSSL 2.5.0
debug1: Reading configuration data /Users/jdoe/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug2: resolving "192.168.0.16" port 2200
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to 192.168.0.16 [192.168.0.16] port 2200.
debug1: connect to address 192.168.0.16 port 2200: Operation timed out
ssh: connect to host 192.168.0.16 port 2200: Operation timed out

netcat also times out:

$nc -w 1 -v 192.168.0.16 -z 2200
nc: connectx to 192.168.0.16 port 2200 (tcp) failed: Operation timed out

But hey, ping (which is a different protocol) works:

$ping 192.168.0.16
PING 192.168.0.16 (192.168.0.16): 56 data bytes
64 bytes from 192.168.0.16: icmp_seq=0 ttl=64 time=97.027 ms
64 bytes from 192.168.0.16: icmp_seq=1 ttl=64 time=4.329 ms
64 bytes from 192.168.0.16: icmp_seq=2 ttl=64 time=2.402 ms
^C
--- 192.168.0.16 ping statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 2.402/34.586/97.027/44.159 ms

What am I missing? What's in my way?

Answer 1

You have a firewall running, since iptables -S's output is about two screens long. But, the rules in the existing firewall are configured for sshd listening on tcp port 22. To make a long story short, the wrong way to fix this -but good for testing and learning purposes- is to simply type sudo iptables -P INPUT ACCEPT and voila, you can connect with ssh.

Afterwards, you had better tell your firewall that ssh is listening on port 2200 instead of 22, and you'll be done for good. It could be that docker deploys its own firewall, so you could have a look in its configuration files and see if you can change from there the sshd port.