My mongo server on Digital Ocean (DO) appears to be accepting connections correctly, but my PC does not see the ip & port as open with an nmap. The server is receiving connections without issues from a different server on DO.

What is especially odd is that this was working perfectly fine and suddenly stopped.

There is a small possibility that this is interfering - I setup port forwarding and DynDNS with my router. “Small possibility” because i’m 85% sure I had this issue before setup of port forwarding & ddns. I thought it was just the changing of my local ip address and I would just need to add it to the mongo server ufw again.

On the Mongo Server

ufw status

root@mongo:~# ufw status
Status: active

To                         Action      From
--                         ------      ----
22/tcp                     LIMIT       Anywhere                  
80/tcp                     ALLOW       Anywhere                  
443/tcp                    ALLOW       Anywhere                  
27017                      ALLOW       [-- other server ip address that works --]          
27017                      ALLOW       [-- local machine ip address --]           
OpenSSH                    ALLOW       Anywhere                  
27017                      ALLOW       Anywhere                  
27017                      ALLOW       [-- local public ip address --]              
22/tcp (v6)                LIMIT       Anywhere (v6)             
80/tcp (v6)                ALLOW       Anywhere (v6)             
443/tcp (v6)               ALLOW       Anywhere (v6)             
OpenSSH (v6)               ALLOW       Anywhere (v6)             
27017 (v6)                 ALLOW       Anywhere (v6)   

nmap

root@mongo:~# nmap [-- mongo server ip address --] -p 27017

Starting Nmap 7.60 ( https://nmap.org ) at 2020-08-05 17:32 UTC
Nmap scan report for mongo ([-- mongo server ip address --])
Host is up (0.000036s latency).

PORT      STATE SERVICE
27017/tcp open  mongod

Nmap done: 1 IP address (1 host up) scanned in 0.25 seconds

netstat -plnt

root@mongo:~# netstat -plnt 
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      694/systemd-resolve 
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      924/sshd            
tcp        0      0 [mongo ip]:27017        0.0.0.0:*               LISTEN      2040/mongod         
tcp        0      0 127.0.0.1:27017         0.0.0.0:*               LISTEN      2040/mongod         
tcp6       0      0 :::22                   :::*                    LISTEN      924/sshd       

On my Local PC

myusername@mb ~ % nmap [-- mongo server ip address --] -p 27017
Starting Nmap 7.80 ( https://nmap.org ) at 2020-08-05 13:30 EDT
Nmap scan report for [-- mongo server ip address --]
Host is up (0.024s latency).

PORT      STATE    SERVICE
27017/tcp filtered mongod

Nmap done: 1 IP address (1 host up) scanned in 0.43 seconds

There is something going on in between these machines that I haven’t caught. I need this to CRUD my production database locally.

Things I’ve tried:

1. Removing and adding back the ip address from ufw
2. Making 27017 allowed from anywhere (as seen above; previously restricted to only specific ips)
3. Listening for connections on 27017 with nc localhost 27017 (have not heard anything)
4. ufw disable - still returns filtered on local PC.
5. Disabled the DynDNS
6. Added 27017 to my router’s firewall.
7. Testing nmap through a VPN

None of these have worked.