I think it's normal behavior. When you try to access a UDP port on a
server, and nothing is listening for incoming UDP connections, the server
should respond with an ICMP packet type 'UDP port unreachable'. The ICMP
packet will have some information about the original UDP packet it is
responding to in its payload.
NMAP is a good tool for testing ports. Another good one is Netcat. It let's
you do a telnet-like interactive connection to UDP ports. You can also fo a
'netstat -a' if you are logged into the server in question. It should list
all listening and established connections.
----- Original Message -----
From: "Yannick Vansevenant" <yannick.vansevenant,AT,mobyus,DOT,com>
Sent: Tuesday, December 26, 2000 8:51 AM
Subject: port unreachable
> anyone cares to explain a bit on this /var/log/messages ?
> 13:45:46.207280 > callisto.9999 > crux.9999: udp 104
> 13:45:46.540309 < crux > callisto: icmp: crux udp port 9999 unreachable
> Which port is now unavailable ? How can somone in linux check if a port is
> available ? By doing a telnet on it ?
> Thanks !
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