[SNMP4J] Router loop causes all communication to stop

[Tjip Pasma]

Hi
 
I was building a small snmp test application this friday when i stumpled into this problem. 
Part of my application is to run a snmp discovery, this was working just fine until i changed the ip range that the discovery should run within.
Suddenly nothing was working anymore. Using wireshark i discovered that i only was sending to one ip address withinin the range.
I enabled the snmp4j logging features and notiched this:
 Socket for transport mapping org.snmp4j.transport.DefaultUdpTransportMapping$ListenThread at 17431b9 error: socket closed
This exception was thrown from the socket.receive() call. This explained why all further communication was stopped, but i was still 
clueless to the reason for the exception, until i notiched the icmp message "Time-to-live exceeded" in wireshark (from now on im using "udp port 161 or icmp" as wireshark filter :-).
 
This "Time-to-live exceeded" is in this case triggered by a router loop misconfiguration in my network, but i would prefer to be robust to this case. (discovery features is part of our main applications, and router misconfiguration may also happen in a production setup). 
 
So far i can only see 2 solutions to this.
A) Ignore this exception 
Currently the flag "stop" is set to true when this exception is thrown, this causes the listening thread to be shut down and the socket to be closed.
I did a few test with this and appearently the socket keeps on running, despite that the exception message is "socket closed". 
This solution worries me since the socket state may be corrupt ?
 
B) start new socket.
As i see it, this would be a larger rewrite of this class, requiering some blocking mechanism while the socket is being replaced.
 
 
Can anyone help with other suggestions to solve this ?
 
 

Best Regards

 

Tjip Pasma
System Engineer

 

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