Unable to get snmp to work consistently on Ubuntu 20.04

I have been struggling to get snmp to work consistently on Ubuntu 20.04. I started on one server and finally got an snmpd.conf configuration that worked on it. I then installed snmp on a number of other Ubuntu 20.04 servers and put the working snmpd.conf file on them but some of them work and the others don't. For the systems that don't I have tried running snmpwalk -v1 -c . It works when I run the command on the servers themselves but when I run it from a different server I get "Timeout: No Response from ".

Output from netstat -an | grep 161 shows "udp 0 0 0.0.0.0:161 0.0.0.0:*" on all my servers

I can ping the servers from the server that I am running the commands from and I have confirmed that the systems' firewalls are allowing access to port 161. In fact, I have disabled ufw on a couple of the servers just to see it that would make a difference and it didn't. Has anyone else run into this? And more importantly, how did you resolve it?

If snmpwalk responds on the localhost, then snmp is most likely configured properly on the test target.

This state is further confirmed if at least some remote machines are able to query snmp data on the test target.

For those targets that do not respond, it's highly likely that the route to the snmp port is being blocked or the port is closed or otherwise has restricted access. Since you said that you used a copy of the config file from a running snmp client I am going to assume that all machines are using the same port and have the same public (and private) community string.

Of course the above may not be true so check to make sure that snmpwalk is given all the correct access information needed to query the MIB.

On the remote machine that is unable to access the target snmp data, install nmap if it isn't already installed.

sudo apt update
sudo apt install nmap

Verify that the snmp listening port responds

nmap <target hostname or ip address>

Example:

frankie@ubuntu-m8h:~$ nmap 192.168.0.9
Starting Nmap 7.80 ( https://nmap.org ) at 2023-03-16 15:31 PDT
Nmap scan report for 192.168.0.9
Host is up (0.00017s latency).
Not shown: 996 closed ports
PORT    STATE SERVICE
22/tcp  open  ssh
25/tcp  open  smtp
161/udp open  snmp
514/tcp open  shell
631/tcp open  ipp

The correct usage of snmpwalk is:

snmpwalk  -r:<device_IP> -c:<community string>  -v:<SNMP version>

If the snmp port responds but a snmpwalk times out, check to make sure that the community string matches (public is the default community string).

It's a best practice to initially install snmp using the defaults. Do not change ports or community strings until proper operation has been confirmed. It is wise to change the private community string before starting snmpd though.