Background
UDP Ping is really useful especially to see if SNMP is running. The syntax for UDP checking commands is a bit obscure so we’ve listed a few variants.
NMAP
SNMP running on port 161 UDP, but open and filtered:
➜ ~ sudo nmap -sU -p 161 xyz.vander.host Starting Nmap 7.80 ( https://nmap.org ) at 2022-02-09 11:01 SAST Nmap scan report for xyz.vander.host (x.y.z.v) Host is up (0.022s latency). PORT STATE SERVICE 161/udp open|filtered snmp
SNMP running on port 161 UDP, but just open:
➜ ~ sudo nmap -sU -p 161 abc.vander.host Starting Nmap 7.80 ( https://nmap.org ) at 2022-02-09 11:01 SAST Nmap scan report for abc.vander.host (a.b.c.d) Host is up (0.023s latency). PORT STATE SERVICE 161/udp open snmp
NC
nc is also known as nmap-ncat. Here is the command syntax to test if an UDP port is listening with nc. Be sure to use the v verbose switch to get the full story.
nc -zvu serverxyz.abc.com 161 Connection to serverxyz.abc.host 161 port [udp/snmp] succeeded!
Or try this (not working version – see 0 bytes received):
[root@872397-db1 ~]# nc -zvu 127.0.0.1 161 Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to 127.0.0.1:161. Ncat: UDP packet sent successfully Ncat: 1 bytes sent, 0 bytes received in 2.01 seconds.
And here are some alternate methods:
sudo nmap -sU -p port target nping –udp -p port target hping3 -S –udp -p port target
https://www.tecmint.com/check-remote-port-in-linux/