[SNMP4J] Invalid trap checksum??

[Neil Cohen]

I have created a java program using SNMP4J which generates and sends an 
SNMP v1 trap. The basic code looks like this:

private void sendTrap(String alertMsg) {
         OID oid = new OID("1.2.3.4.5.2");

         try {
             PDUv1 pdu = new PDUv1();
             pdu.setType(PDU.V1TRAP);
             pdu.setAgentAddress(new IpAddress("2.2.2.2"));
             pdu.setGenericTrap(PDUv1.ENTERPRISE_SPECIFIC);
             pdu.setSpecificTrap(1);
             pdu.setEnterprise(oid);
             pdu.add(new VariableBinding(oid, new OctetString(alertMsg)));

             CommunityTarget comTarget = new CommunityTarget();
             comTarget.setCommunity(new OctetString(snmpCommunity));
             comTarget.setVersion(SnmpConstants.version1);
             comTarget.setAddress(new UdpAddress("1.2.3.4/162"));    // 
Host address is actuall a valid address...
             comTarget.setRetries(2);
             comTarget.setTimeout(5000);

             TransportMapping transport = new DefaultUdpTransportMapping();

             Snmp snmp = new Snmp(transport);
             snmp.send(pdu, comTarget);
             snmp.close();
             transport.close();
             transport = null;

             Logger.info("SNMP sent...");
         } catch (Exception e) {
             Logger.error("Exception: " + e);
             e.printStackTrace();
         }
     }

I ran tcpdump on the receiving system and got this:

[root at nbc-verisign ~]# tcpdump -vvv port 162
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 
65535 bytes
10:41:34.724763 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto 
UDP (17), length 357)
     nbc.vrsn.com.49834 > 1.2.3.4.snmp: [bad udp cksum 52d!]{ SNMPv1 
C=<communityString> { Trap(310)  .2.11etc. etc.

The incoming string looks to be correct. But I'm concerned about the 
'bad udp cksum' section. Is there a way to create the checksum before 
the message is sent? If not, what would be the error here, and how do I 
correct it??

thanks very much,

nbc

-- 

NAME:   Neil B. Cohen (Verisign Inc.)
PHONE:  703-948-4471
DOMAIN: ncohen at verisign.com
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* Murphy's Philosophy: Smile - tomorrow will be worse...
*
* O'Tooles Commentary: Murphy was an optimist!
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