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March 2011
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How do I verify UDP port is open or not

This is very rare scenario, you need to verify the status of udp service running on the port. I found this tricks will helpful if you are trying to verify NTP server availability or VPN server presence.

Eg: nmap -p [port] -sU -P0 [host name | ip address]

a. For verify the NTP server is running

[root@fc-web03 ~]# nmap -p 123 -sU -P0 192.168.10.16

Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2011-03-28 13:28 EDT
Interesting ports on 192.168.10.16:
PORT    STATE         SERVICE
123/udp open|filtered ntp
MAC Address: 00:18:8B:48:7F:8B (Unknown)

b. For verifying VPN server is running

[root@fc-web03 ~]# nmap -p 1194 -sU -P0 141.73.12.62
Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2011-03-28 13:30 EDT
Interesting ports on 141.73.12.62:
PORT     STATE         SERVICE
1194/udp open|filtered unknown

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